Where and when Arctic Skua breeds in n. and w. Scotland but is a widespread coastal migrant, mainly in April/May and August to October (with a few lingering into winter). Pomarine Skua is an uncommon migrant, mainly in late April/May and August to November but, unlike the other two species, small numbers regularly occur throughout the winter, particularly in the North Sea. Most are seen on spring passage, when variable numbers move up the English Channel and also north through the Irish Sea. The vast majority, however, move up the Atlantic and, during strong north-westerly winds, large numbers may be seen off the Outer Hebrides and nw. Ireland. Long-tailed is by far the rarest skua (about 370 records a year in 1981–90) but breeding has been attempted. Like Pomarine, the vast majority move up the Atlantic, and north-westerly winds may also produce a large spring passage off the Outer Hebrides. Otherwise, small numbers are most likely to be encountered in August/September, mainly off North Sea coasts (it is very rare in the English Channel). A huge autumn movement in 1991 produced a British record for that year of 5,350, mainly in the North Sea (Fraser & Ryan 1994). All three species can appear inland; in fact some routinely migrate overland, appearing on fresh water and even in fields (the latter mostly Long-tailed) particularly during gloomy anticyclonic weather. Such birds may be incredibly tame.
General approach Skuas are exciting birds that always enliven a sea watch but, with the exception of adults in summer plumage, the three smaller species are notoriously difficult to identify. Any discussion of their identification is complicated by their variability. Firstly, adult Arctics and Pomarines have pale and dark plumage morphs (as well as intermediates). Secondly, juvenile plumages of all three species are similar, and individual variation at this age is considerable. Thirdly, skuas do not reach maturity until about three to five years old. As they usually remain in their winter quarters during their first summer, their immature plumages are unfamiliar to Northern Hemisphere birders. The identification of immatures can also be complicated by bleaching and wear. Fourthly, judging their size is complicated by the fact that females are significantly larger than males (averaging c. 12–15% heavier). Although experienced seawatchers may confidently identify skuas at some distance (largely by ‘jizz’) less-experienced birders should exercise caution and identify only those that are seen well; be prepared to log some as ‘skua sp.’. It is an odd paradox that distant skuas at sea are routinely identified with confidence, even by inexperienced birders, yet close-range birds inland often prove controversial. In view of the complexities of identifying winter adults and immatures, only summer adults and juveniles are dealt with in depth; other plumages are outlined on p. 196. Finally, note that adults retain their summer tail projections throughout the autumn until they moult in their winter quarters, but the projections may be susceptible to loss or damage.
Structure Generally the commonest small skua, this species should act as the yardstick when identifying the other two species. Size intermediate between Pomarine and Long-tailed, being similar to Common Gull Larus canus, but much sturdier. Structural differences from Pomarine and Long-tailed are dealt with under those species but, compared to Pomarine, note Arctic’s medium build, being smaller and slimmer with a longer-looking head, narrower wings and tapered rear end; adults have an obviously pointed tail projection, which may be as long as 10.5cm (4.5 inches) suggesting Long-tailed. Conversely, skuas of all species and ages can occasionally lack central tail feathers, either through moult or damage. At close range, the bill is rather slim and slender, lacking Pomarine’s more obvious gonydeal angle.
Flight Migrating flight is steady, but less heavy and ponderous than Pomarine. All three species glide on distinctly arched wings. In strong winds, Arctic may adopt a shearwater-like flight, rising and falling above the waves in a series of long arcs, but the wings are held more arched than most shearwaters and the arcs tend to be flatter.
Plumage Adult summer Dark-phase adults are commonest and they appear completely dark fulvous-brown; a yellowish shade to the cheeks and ear-coverts is not obvious at any distance. Pale-phase adults have a blackish cap and are mainly white below, usually with a pale yellow face; they often have a brown breast-band of variable width and extent, but generally weaker than Pomarine. At close range, three or four white shafts on the upperwing, at the base of the primaries, are noticeable ( cf. two on Long-tailed) and these show as a pale crescent on the underwing. The upperparts are brown; pale and intermediate birds are warmer-toned than Pomarine or Long-tailed and the upperwing-coverts show little or no contrast with the black secondaries ( cf. Long-tailed, which shows marked contrast). Intermediate adults vary between dark and light phases. Juvenile Except for some very dark birds, juvenile skuas can usually be aged by their barred underwing-coverts and axillaries, blue-grey to pinkish-grey bill base and blue-grey to whitish legs. Plumage tone varies, Arctic and Long-tailed being more variable than Pomarine. The underparts of Arctic vary from uniformly blackish through brown to greyish-white, narrowly barred brownish. Differences from Pomarine and Long-tailed are outlined under those species, but the following are the main characteristics of Arctic. 1 DARK PHASE Note that very dark juvenile Arctics are solidly blackish-brown throughout, lacking any obvious barring (but a few dark Long-taileds can look similar, especially at a distance). 2 FEATHER FRINGES The pale feather fringes on pale and intermediate phases are warm in tone (rufous or buff) and do not contrast with the richer brown background plumage; this renders their entire plumage warmer-toned than Pomarine or Long-tailed (thus appearing ‘foxy-toned’: yellow-brown or rufous-brown). 3 HINDNECK Unlike Pomarine, most have a contrastingly pale hindneck, which is often warm-toned. 4 UPPER- AND UNDERTAIL-COVERTS Although often thickly barred brown and buff, the barring is not especially contrasting so, unlike Pomarine and Long-tailed, they fail to show obviously paler upper- or undertail-coverts. 5 UPPER-PRIMARY PATCH The shafts on the bases of the first three or four primaries are white (only two are white on Long-tailed). 6 UNDER-PRIMARY PATCH There is a single white flash on the under-primaries so, unlike Pomarine, it does not generally show a narrow pale crescent in front of the large pale patch. 7 PRIMARIES At rest it shows noticeable pale tips to the primaries (not shown by Pomarine or Long-tailed). 8 TAIL PROJECTIONS Short and pointed (always blunt on Pomarine; blunt and usually longer on Long-tailed). 9 BILL Usually rather uniformly dark, lacking an obviously paler base.
Structure Summer-plumaged adults are most easily identified by their blunt, twisted central tail feathers, which look like spoons or legs/feet trailing out behind. These are retained throughout the autumn until their winter moult. However, the ‘spoons’ may be abraded or even broken off by late autumn and even in spring a minority show only slight protuberances. Juveniles lack ‘spoons’ but they have a short, blunt projection (pointed on Arctic); this is quite noticeable in closer views (down to c. 400m) but difficult to see at any distance (and may even be absent). In winter plumage, adults show a short projection that is hardly twisted. With Pomarines lacking ‘spoons’, it is essential to concentrate on overall size and structure. Although size evaluation may be difficult with lone birds, Pomarine is a large skua, approaching Lesser Black-backed Gull L. fuscus (about four-fifths the size in direct comparison) or c. 10% larger than Common Gull (Arctic is more similar in size to the latter). It is a sturdy, thickset, powerful and ‘meaty’ bird with a large head, a chunky body and a shorter-looking rear end; note also the heavy, hooked bill. Most importantly, the wings are broad-based and it has a sturdy, robust appearance in flight (in direct comparison, Arctic Skua is smaller, noticeably slimmer and flatter-chested); on summer adults, the deep-chested appearance may be emphasised by a thick dark breast-band. They may also show a more ragged appearance to the vent. Juveniles or dark-phase adults can be confused with Bonxie S. skua, a mistake unlikely with Arctic. On the ground, they again look big and bulky with a relatively short primary projection.
Flight Even in direct comparison there may little difference in their flight action. However, Pomarine generally has a slightly slower, steadier, more ponderous and more lumbering flight than Arctic, with continuous gull-like flapping low over the waves – often ‘hugging’ the sea – interspersed with short glides on bowed wings. Thus, the flight is not as ‘fast and dashing’ as Arctic. Like that species, it shears in long arcs during strong winds. When pursuing prey, the wingbeats are deep and bowed. Unlike the smaller skuas, it habitually kills and eats quite large birds, such as smaller gulls. It also chases larger birds for food, such as Herring L. argentatus and Lesser Black-backed Gulls, and may even force them into the sea. Like Bonxie, it often feeds on scraps.
Plumage Adult summer Approximately 90% of adults are pale phase. Apart from the tail ‘spoons’ no single character separates Pomarine from Arctic, but ‘Pom’ is generally darker, blacker-brown above, and usually has a prominent dark breast-band (but some, mainly males, just show patches on the breast-sides). It also has larger whitish wing patches as well as a greater incidence of flank barring (but beware of the superficial similarity between adult Pomarine and subadult Arctic). The extensive white face (extending onto the nape) is usually obvious at all ranges, and this is usually (but not always) washed pale yellow, visible at some distance. Dark-phase birds are completely dark brown and very striking, but their whitish wing flashes may appear less obvious than on pale birds. Many ‘Poms’ retain traces of winter plumage well into summer and such intermediate individuals appear much duskier below, especially at a distance. Juvenile The main differences from Arctic are as follows. 1 PLUMAGE TONE Pomarine is fairly consistent in plumage tone, being generally rather dark brown, with no warmth to its plumage. The body plumage is variably barred buff (strongest on pale-phase individuals) and the barring is better defined than on Arctic. 2 UNDERWING CRESCENT One of the best plumage features is a whitish crescent in front of the large and very obvious silvery-white patch at the base of the under-primaries; the crescent is formed by pale bases to the greater under-primary coverts and, in good light, is visible at long range. Arctic may show a faint, diffuse crescent in front of the under-primary patch, but this is hardly visible in the field. The white flash on the upperwing is less obvious. 3 TAIL-COVERT BARRING Strong brown-and-whitish barring on the uppertail-coverts forms a noticeable pale ‘rump’ in flight; the undertail-coverts, vent, lower belly and, sometimes, the flanks, are similarly barred. The equivalent barring is less contrasting and less obvious on Arctic, and note that dark Arctics usually lack barring altogether. 4 BILL Longer and heavier than Arctic, with a more prominent gonydeal angle. The basal two-thirds are pale bluish, olive or sandy, contrasting with the dark tip (recalling juvenile Glaucous Gull Larus hyperboreus); the pale base may ‘flash’ paler at a distance. Arctic’s bill base is less prominent because (a) it is usually slightly darker, (b) the bill is smaller and (c) the adjacent head feathers are paler and do not contrast with the base. 5 HEAD Drab grey-brown, rarely showing Arctic’s contrastingly pale hindneck (but may show a paler grey wash). Thus, wholly brown-headed birds with barred underparts are almost certainly Pomarine. The few Arctics that lack a contrasting light hindneck are usually solidly blackish-brown, with unbarred underparts. Dark streaking on the head is typical of Arctic and is never present on Pomarine, which instead is lightly barred. 6 TAIL PROJECTIONS Short and rounded (always short and pointed on Arctic); some Pomarines lack projections altogether. 7 LEG COLOUR There is overlap in leg colour: bluish-grey, and all three species may show whitish legs. Second-winter See ‘Appendix’ p. 196.
Structure Although there is size overlap, Long-tailed is as different from Arctic as Arctic is from Pomarine. A small skua, similar in size to Black-headed Gull Chroicocephalus ridibundus. Adults are readily identified by their incredibly long central tail feathers which waver in flight. They can have streamers up to 18cm (7 inches) in length but note the overlap with Arctic, which can have projections up to 14cm (5.5 inches). However, Arctic’s tail tends to appear thick and tapered, whereas Long-tailed’s projections are obviously long and thin (the two separate feathers are often clearly visible). Juvenile Long-tailed has a short to medium blunt tail projection (see below). Unlike the other skuas, it has no bulk to its body, being slimmer with a shallower breast; on the water, it appears slim and elongated. It has a smaller bill than Arctic, with less of a gonydeal angle, and a smaller, more rounded head. This combines to produce a much gentler character and appearance, perhaps recalling Common Gull.
Flight Narrower wings than Arctic, especially at the base, and often appears light, slim and agile, the whole effect being more tern-like. It tends to have a more continuously flapping flight, with little gliding, and may even feed with small gulls, dropping down to the water’s surface to pick up food. Inland birds may pick insects off the water or even hawk them in the air; others have fed on earthworms in ploughed fields.
Plumage Adult summer Do not rely solely on tail length, but concentrate on structure and plumage. Long-tailed is more consistent in its appearance than Arctic and even Pomarine: dark-phase birds are very rare and intermediates virtually unknown. Typical adults differ from Arctic in the following respects. 1 CAP Neat, clear-cut and black, contrasting sharply and smartly with the white face (often washed pale primrose-yellow). 2 UNDERPARTS White, lacking a breast-band, but lower belly and vent obviously dark (ashy-grey, like upperparts) merging but contrasting with the obvious white upper breast and face (sometimes the dark belly extends up to the lower breast). Therefore, the front end looks white, the rear end dark. However, some are much whiter-bellied (mainly from Greenland, North America and E. Siberian populations, race pallescens). 3 UPPERPARTS Cold ashy-grey, not as dark as Arctic. The primaries and secondaries are black, the latter contrasting with the wing-coverts to form a noticeable dark trailing edge to the wing (Arctic appears plain brown above). The tail is black, contrasting with the paler rump and uppertail-coverts. 4 upper-primary patches Significantly, there is little or no white in the upperwing: usually just two white primary shafts (Arctic has white bases to three or four, forming a definite patch). 5 UNDERWINGS Dark silvery-grey with a contrasting black border to the front and rear of the wing; as on the upperwing, just two pale shaft-streaks on the outer primaries. Juvenile Exhibits a variety of plumage tones, from pale through intermediate to dark. Paler individuals can be separated from Arctic by the following differences. 1 PLUMAGE TONE Generally colder and greyer-looking than Arctic. 2 UPPERPART BARRING Upperparts show clearly defined cream or whitish barring, contrasting with the grey-brown background colour, producing a neat, scaly effect at a distance (Arctic has darker, buffier barring that contrasts less with the browner plumage, producing a warmer tone to the upperparts). 3 UPPERTAIL-COVERTS In flight, heavy brown and whitish barring produces a noticeable whitish ‘rump’ (duller and less obvious on Arctic, some having plain upper- and undertail-coverts, never found on Long-tailed). 4 TAIL PROJECTIONS Blunt-tipped; length varies from short to medium. Always short and pointed on Arctic, so those Long-tailed that show longer projections are quite distinctive, although the projection can be difficult to make out at a distance. Beware of Arctic Skuas that lack central tail feathers, the two adjacent ones then appear to be blunt central feathers. 5 PRIMARY PATCHES Only one or two white primary shafts (although white on the bases of the third and fourth may be perceptible at point-blank range). On Arctic, three or four show obvious white. Consequently, Long-tailed shows little white on the upperwing, but has a larger broad pale whitish-grey crescent-shaped patch on underwing. 6 UNDERPARTS Typically greyish, with finely barred flanks; many show a darker head and neck, with a large whitish area immediately below. Undertail-coverts strongly barred. 7 HEAD A pale greyish area on the sides of the head and nape shows to a greater or lesser degree. Some pale individuals are strikingly white-headed. 8 UNDERWING-COVERTS Heavily barred, especially on the axillaries (some darker Arctics have uniform underwing-coverts, never found on Long-tailed). 9 BILL Generally more black at tip (40–50% of bill is black, compared with 25–30% on Arctic) and the black usually extends back past the gonydeal angle and frequently tapers along the cutting edge, about halfway into grey base. 10 PRIMARIES Unlike Arctic, it lacks buff fringes to the tips of the closed primaries, which appear plain black at rest. Dark juveniles Much more similar to dark Arctic but they show more contrastingly pale buff feather fringes to the upperparts (although some are very finely patterned and look wholly dark at a distance). However, on closer birds, quite striking dark brown-and-white barring on the undertail-coverts should be obvious, both at rest and in flight.
Owing to the complexities of identifying winter adults and immatures, it must be stressed that the following details are generalised. Adult winter On failed breeders, winter plumage starts to appear from July onwards and may be complete by August, but for most the moult starts from late August and is completed in the winter quarters. Unlike most juveniles, winter adults lack underwing-covert and axillary barring, and have a black bill and legs. On pale-phase birds, the cap becomes less distinct and the throat and neck duskier. The upperparts feathers show pale fringes and the tail-coverts are barred, as on juveniles. Dark-phase individuals are more similar to summer adults, but may acquire indistinct barring on the tail-coverts. All adults have shorter tail projections in winter, while moulting individuals may temporarily lose them altogether. Immatures Owing to our incomplete knowledge, the following gives only an outline and it should be stressed that immature skuas are notoriously variable, a problem exacerbated by wear and bleaching. The following details relate to Arctic Skua (from BWP), but the sequence appears similar for all species, although Pomarine appears to take a year longer to reach maturity. Juvenile plumage is moulted in midwinter and ‘first-winter’ plumage is characterised by a mixture of adult winter (including slightly longer tail projection) and juvenile characters (such as pale legs and, on pale-phase birds, barred underwing-coverts and axillaries). Dark-phase ‘first-winters’ are more similar to juveniles, but on average less heavily barred. ‘First-winter’ plumage is retained until late summer, when it is replaced directly by second-winter, so there is no first-summer plumage. In their second summer, some skuas arrive at the breeding colonies with variable amounts of adult-like summer plumage mixed with second-winter plumage. From then on, the moults gradually produce a more adult-like plumage until maturity, and traces of winter plumage are no longer retained in summer. However, some fully mature adults (mainly Pomarines) retain traces of winter plumage on arrival on the breeding grounds. Some mature earlier, so ageing is very difficult once juvenile characters are lost (such as the pale legs and partially barred underwing-coverts and axillaries).
Appendix Second-winter Pomarine Skua Given Pomarine’s propensity to winter around our coasts, the following details may be useful, based on a well-studied November individual. Uniformly dark brown upperparts, head and breast, the latter producing a hooded effect in flight (with a slight dark cap). Belly silvery-white but flanks and undertail-coverts heavily barred pale buff. Pale tips to the uppertail-coverts formed a noticeable pale ‘rump’ in flight. Noticeable blunt tail projection. Underwing-coverts plain brown (barred on juvenile) and legs and feet largely blackish (obviously pale bluish-grey on juvenile, sometimes whitish). Plumage less immaculate than juvenile, with clear signs of inner primary moult. The narrow whitish crescent in front of the large whitish under-primary flash was faint. Bill appeared ‘blob-ended’, the black tip contrasting with a slightly paler base.
References Broome (1987), Davenport (1987), Fraser & Ryan (1994), Jonsson (1984), Mather (1981), Olsen & Christensen (1984), Stoddart (2012), Ullman (1984).
Where and when Kittiwake is a common coastal species throughout the year, but rarer in winter; it also migrates overland and small numbers (occasionally large flocks) may appear on inland lakes and reservoirs, mainly in March/April and September/October. Little Gull is a scarce passage migrant, mainly from March to May and August to October, but smaller numbers are encountered throughout the year; it is much more likely to be seen inland than Kittiwake. Large numbers occur at selected coastal sites, notably in the North Sea, with over 6,000 sometimes gathering off the Yorkshire coast. Sabine’s Gull is a rare autumn passage migrant from Canada, mainly in September/October, with occasional spring occurrences from March to June; it is extremely rare in winter. It currently averages 165 records a year, with a peak of 710 in 1987. Most records are from the west coast, particularly Cornwall (and w. Ireland) but it can occur in any coastal county and even inland; numbers depend on the prevalence of westerly gales and large movements or ‘wrecks’ sometimes occur.
Flight identification Juvenile and first-winter are superficially similar to the equivalent plumages of Little Gull, both species showing a large black ‘W’ across the wings in flight. Kittiwake is much larger than Little Gull, being slightly larger than Black-headed Gull Chroicocephalus ridibundus. The grey mantle, scapulars and leading wing-coverts are quite dark, highlighting the extreme whiteness of the inner primaries and secondaries. Also, the black ‘W’ is better defined, particularly on the primaries: this combination produces a smarter, more contrasting ‘grey-black-white’ pattern than first-winter Little Gull. Juvenile and first-winter Kittiwakes are similar, but the juvenile has a prominent black collar across the nape, which is usually lost in first-winter plumage (when it may show a grey shawl instead). A thick black bill contrasts strongly with the white head, which has a black spot or smudge behind the eye. The underwing is snowy white, with contrasting black tips to the under-primaries; the very white primaries and secondaries appear translucent from below. By spring, it lacks the black collar and the plumage wears and fades considerably, so that the outer primaries are not as black, the mantle and wing-coverts are paler grey and the general appearance is whiter and less contrasting; later in summer, some may become severely bleached and abraded.
Identification at rest In fresh plumage, looks smart and contrasting. Identified by its thick black bill, predominantly white head, black collar (when present), rather dark grey mantle and scapulars, and large black bar across the base of the wing-coverts, extending onto the tertials. Note also the black legs, which are very short for a gull.
Flight identification A tiny gull, about two-thirds the size of Kittiwake; its small size is usually obvious, even without other species for comparison. Its feeding behaviour is remarkably tern-like, flying back and forth and dipping down to the water like a Black Tern Chlidonias niger (Kittiwake is more typically ‘gull-like’). Juvenile is easily separated from Kittiwake as the back and scapulars are completely blackish (the feathers edged pale) and this coloration extends onto the nape and neck-sides; the crown and ear-coverts are also black, quite unlike Kittiwake. As autumn progresses, however, it moults into first-winter plumage, the black feathering on the mantle and scapulars being replaced by grey, while the nape becomes white; at certain stages of moult, it can show the effect of a dark collar, suggesting Kittiwake, but this is rarely as clear-cut. First-winter retains the distinctive dark crown and ear-coverts that Kittiwake lacks; in flight, it looks less contrasting than Kittiwake, the greys contrasting less with the whites, and the black on the primaries is less clear-cut (the underwing too is a less pure white). First-summer may acquire a partial black hood.
Identification at rest Juvenile is easily identified by its predominantly black upperparts, crown and ear-coverts; this attractive black-and-white plumage suggests a large juvenile phalarope Phalaropus. First-winter is more like Kittiwake but, again, is easily separated by its black crown and ear-coverts, less contrasting upperparts, the small, delicate bill, and short pinkish-red legs.
Call A quick, throaty, tern-like ar – akar akar akar akar, recalling a squeaky toy (first-year Kittiwakes are relatively silent).
Black-winged Little Gulls There are records of atypical first-year Little Gulls with the whole upperwing black (with paler feather fringes) leaving a prominent white trailing edge; in first-winter, these show a grey mantle and scapulars that stand out as a pale ‘saddle’.
A very distinctive gull, easily identified if seen well. Despite this, many claimed Sabine’s, particularly distant individuals on sea watches, are misidentified Kittiwakes. Caution is therefore essential.
Size and structure In direct comparison, Sabine’s is noticeably smaller than Black-headed Gull and has long, thin, pointed wings; it has a tail fork but this is difficult to see at any distance. On the ground, short legs produce a pigeon-like gait. Adult summer In early autumn (August/early September) most Sabine’s passing offshore are adults and most retain a full black hood (by late autumn, this is often reduced to a large black smudge across the rear of the head). The combination of black hood, black primaries, dark grey mantle/wing-coverts and the huge white triangle on the inner primaries/secondaries permits instant recognition. The underwings are pure white, with dark tips to the primaries (often with a thick greyish bar across the greater underwing-coverts). Juvenile Dark grey-brown mantle and wing- coverts (with noticeable scaling at close range, caused by narrow whitish feather fringes) and extensive washed-out grey-brown on the nape and breast-sides. The latter two areas produce an obvious dark ‘front-end’ to the bird in flight. The brown areas, along with the black primaries, contrast strongly with the white triangle on the rear of the wing. The underwing is white but has noticeable grey shading on the under-primaries and a broad dark greyish bar across the greater underwing-coverts. Juvenile Sabine’s therefore lacks the black ‘W’, grey mantle, black collar and predominantly white head of juvenile/first-winter Kittiwake. Note that juvenile Sabine’s do not moult until they arrive in their winter quarters. Winter adult and first-summer Sabine’s Gulls do not normally occur in the Northern Hemisphere in winter, so observers should not claim a winter Sabine’s unless it is seen exceptionally well. Winter adults resemble summer birds but show a greyish or blackish ‘half-hood’ from the eye over the rear of the crown. First-years usually remain in the winter quarters during their first summer, but individuals occasionally move north in spring. At this time, such birds have a grey back and scapulars (forming a grey ‘saddle’) contrasting with the worn brown wing-coverts; they also show brown smudging on the rear crown and nape (plus a brown spot behind the eye) and pinkish legs. The overall appearance at rest may suggest a huge winter-plumaged Grey Phalarope Phalaropus fulicarius. By spring, such birds have already started wing and tail moult. By late summer, first-years are adult-like but have variable messy grey shading over the crown and/or nape, advanced birds showing a ‘moth-eaten’ hood.
Behaviour Sabine’s often flies on noticeably bowed wings. When feeding over the water, it has a flapping flight before stalling and dropping to the surface with the wings raised almost vertically.
Where and when Formerly an irregular vagrant, Mediterranean Gull Larus melanocephalus has spread across n. Europe and is increasing. In Britain, over 1,000 pairs bred at c. 34 sites in 2010, the largest colonies in Hampshire, Kent and Sussex (Holling et al. 2012). It has also bred in Ireland since 1995. Small numbers are widespread outside the breeding season, both on the coast and inland, but it is rarer in n. England and Scotland. Adults disperse from their colonies in late June and return in March or April. Juveniles appear later, generally in July/August, and first-years linger into the summer. Large gatherings occur in some areas, with over 800 recently recorded on the Fleet in Dorset and over 600 in Southampton Water.
Size, structure and behaviour ‘Med Gull’, as it is universally known, is slightly larger, distinctly heavier, chunkier and squarer-headed than Black-headed Gull Chroicocephalus ridibundus (although small individuals, no doubt females, may be similar in size). On the water it looks rather neckless, flat-backed and somewhat less attenuated, while a thick, rather blunt bill is apparent at surprisingly long range. In flight it looks bull-necked and deep-chested with stiffer, less pointed wings, the latter effect perhaps emphasised on adults by their lack of a white primary wedge. It has rather a smooth, high-stepping, plover-like gait and is often markedly aggressive to other small gulls. In spring, it has a distinctive low, soft, deep but far-carrying call: eeuurr or a-ahar, rising and falling slightly (the rhythm vaguely suggesting the call of male Eurasian Wigeon Anas penelope).
Plumage Adult AT REST Easily separated from Black-headed Gull by its prominently white primaries and (in winter plumage) by a large black, wedge-shaped ear-covert patch that often extends as a narrow grey shawl over the back of the head. The head pattern, however, is variable at all ages, some showing less extensive markings, while a small minority lack obvious markings altogether, looking peculiarly white-headed. In summer plumage (usually attained in March) the hood is black (brown on Black-headed) and extends further down the nape than on Black-headed (but this varies with posture). There is also a prominent broken white eye-ring. The thick, blunt bill is usually bright red and close views should reveal a black subterminal band and small yellow tip, but it may fade to orangey-red or even dull orange in autumn. IN FLIGHT A beautiful, ghostly white bird. Unlike Black-headed Gull, the underwings are pure white, while the upperwings shade from pearly grey on the mantle and wing-coverts to pure white on the primaries, lacking both the white primary wedge and black primary tips of Black-headed. The only real pitfall is the very occasional aberrant white Black-headed Gull, Common Gull L. canus or Kittiwake Rissa tridactyla (see below). Second-year As adult, but with variable amounts of black on the primaries. Most have relatively small subterminal markings, often showing as black arrowheads on the closed wing, but others have larger black primary wedges and are less easy to pick out at rest from Black-headed Gulls; however, unlike that species, they usually show prominent white within the black. First-year At rest, does not always stand out from Black-headed Gulls, but look for the combination of the black ear-covert wedge, heavy blunt bill and thickset appearance. The bill is black at first, gradually acquiring a pinkish, orangey or reddish base as winter progresses. Compared to first-winter Black-headed, the closed wing shows browner coverts, solidly dark tertials (only narrowly fringed white) and solidly dark primaries; these plumage differences, combined with the structural ones, produce a unique ‘jizz’ that is very distinctive once learnt. In first-summer plumage, they may gain at least a partial black hood (even full) and the upperparts become pale grey as the dark-centred wing-coverts and dark tertials are replaced. In flight, it has a similar pattern to first-year Common Gull and, when seen with that species, it can be surprisingly difficult to pick out but, again, look for the black ear-covert patch. The wings are, however, cleaner-looking and more contrasting than Common: the primary wedge and secondary bar are blacker, and the mid-wing panel (greater coverts and inner primaries) is clean grey; also, it lacks Common Gull’s obvious dark grey ‘saddle’ (back and scapulars), the mantle being a pale pearly grey. Most distinctive are the underwings: unlike Common, the underwings lack brown markings and are cleanly white, the only real dark being at the under-primary tips. Structural differences, particularly the bull-neck and shorter, stiffer wings, are also useful. Juvenile Even for observers familiar with first-winter Mediterranean Gulls, their first juvenile may come as a surprise. Quite unique, being closest to juvenile Common Gull at rest, as well as in flight. The whole of the upperparts, including the hindneck, are dark chocolate-brown, each feather neatly and cleanly fringed with white, producing an attractively scalloped appearance. The greater coverts, however, are plain grey, standing out as a broad, pale unmarked strip along the base of the closed wing. The breast has brown mottling, concentrated mainly at the sides. Also of note is that, unlike first-winters, the white head is relatively unmarked, with no real wedge and only a faint grey suffusion behind the eye and over the rear crown. The thick black bill is prominent against the featureless head, while the legs are also noticeably dark, reddish-black. The flight pattern is contrasting and similar to first-winter, except that the mantle is blackish, not grey. In comparison, juvenile Common is browner and less contrasting: it lacks the pale greater-covert panel, has extensive brown underpart mottling, a weak bill (with at least some pale at the base), round head, gentle expression and, most importantly, pale greyish or flesh-coloured legs. At rest, Common also looks long-winged and short-legged. Juvenile plumage of both species is quickly lost from early August onwards, during the post-juvenile body moult.
Pitfalls Hybrids When identifying second-years, always bear in mind the remote possibility of hybrid Black-headed × Mediterranean Gull, which shows characters intermediate between the two and may be confusable in a cursory glance: note particularly the hybrid’s slimmer bill and slighter build, as well as traces of Black-headed Gull plumage (such as a hint of a white primary wedge and black tips to the trailing edge of the primaries). Leucistic gulls All-white Black-headed and Common Gulls, and Kittiwakes are not unusual but their sheer whiteness, particularly across the mantle and wing-coverts, instantly separates them from Mediterranean; structural differences and bare-parts coloration are also helpful. Moulting Kittiwakes Another potential pitfall is late summer adult Kittiwakes: when still growing their outer primaries, such birds have shorter, more rounded wings than usual, with the amount of black at the tip severely reduced (perhaps suggesting second-winter Mediterranean).
Where and when A North American gull, first recorded in Britain in 1973, but currently averaging c. 60 records a year, with a peak of 108 in 1992. Most are in seen in western areas, but records have occurred throughout the country. Some have returned to the same wintering sites for many years. Although records have occurred in every month, first-years appear mainly from November to February, often remaining to summer (note that first-years are extremely unlikely before November). Adults and second-years occur mainly from November to April. All age groups also show a marked spring passage, with a peak in March and April; these are thought to be northward-bound birds that have wintered further south.
General approach Ring-billed Gull Larus delawarensis should be identified with caution, especially in first-year plumages; most are found by experienced observers who habitually scrutinise their local gull flocks. A thorough understanding of all plumages of Common Gull L. canus and Herring Gull L. argentatus, including their abnormalities and idiosyncrasies, is essential. The following details outline its separation from the similar Common Gull; differences from Herring are summarised at the end.
Size, structure and behaviour Ring-billed is always conspicuously smaller than Herring Gull, and basically resembles a large Common Gull. However, the size of all three species varies. Some male Ring-billed are noticeably larger than most Common Gulls, while small females are about the same size (comparisons should always be made with several individuals of the commoner species). Ring-billed is slightly different structurally, looking stockier, bulkier and deeper-chested, while on the water it looks flat-backed, sleek and attenuated compared to Common. The most obvious structural difference is the bill, which looks longer, noticeably thicker and more ‘parallel’: this effect is apparent even at a distance, when a thick black band (or tip) makes the bill appear rather blunt. The head is slightly more angular, less rounded than Common, but this has been over-emphasised and the head shape depends largely on attitude: when relaxed, Ring-billed can look quite round-headed. The size difference may be more obvious in flight, when Ring-billed looks distinctly longer- and broader-winged than Common. The wing-tips appear more pointed than those of Common but on adults and second-years this is emphasised by differences in the wing-tip pattern (see below). The legs are often noticeably longer than Common, resulting in a strutting walk . Ring-billed Gulls are often attracted to man and may become very tame.
Plumage Adults at rest Always remember that winter adult and second-year Common Gulls, and second- and third-year Herring Gulls, often show a prominent, clear-cut ring on the bill. The best way to pick out an adult or a second-year Ring-billed at rest is by a combination of mantle colour and tertial and wing-tip patterns. 1 MANTLE Noticeably paler than that of Common, being closer in shade to that of Black-headed Gull Chroicocephalus ridibundus. 2 TERTIALS Rather square and lack Common’s conspicuous broad white crescent. At close range, the tertial tips on Ring-billed are whiter, but they are narrow and do not contrast with the paler mantle. 3 PRIMARIES The closed primaries look uniformly black, with three inconspicuous white primary tips that decrease in size towards the wing-tips (unlike Common, the large white mirrors on the outer primaries are not readily apparent at rest). The pale mantle and black primaries, unrelieved by an obvious white tertial crescent, produce a pattern quite distinct from adult Common, and quite similar to adult Black-headed Gull. 4 PITFALLS Two pitfalls need to be considered: (1) unusually pale Common Gulls do exist, and (2) second-year Commons often show a narrow tertial crescent and little white in the primaries. Make sure that your ‘adult Ring-billed’ is not a second-year Common. To avoid such pitfalls, it is absolutely essential for the identification to be confirmed by other features. Structural differences, outlined above, are especially important, and pay particular attention to the bill. 5 BILL The black band should stand out clearly and cleanly, and contrast with the pale yellow base, even in winter. 6 EYE COLOUR A key difference: Ring-billed has pale irides (as well as a narrow orange orbital-ring) but the pale eye is difficult to detect at any distance. However, it usually produces a squint-eyed expression, in contrast to the dark-eyed, open-faced look of Common. 7 HEAD STREAKING Ring-billed tends to have paler, mottled head streaking, but some show quite dark streaking (this is so variable on Common as to render it of limited value in the field). 8 LEGS Often yellower.
Adults in flight If a suspected Ring-billed flies or wing-flaps, concentrate on the wing-tip pattern: Common has two large, conspicuous white mirrors right across the wing-tip, but on Ring-billed the mirrors are small, relatively inconspicuous and often confined to just one mirror on the inner web of the outer primary (the relative lack of white emphasises the more pointed wing shape). The pale mantle and wings contrast strongly with the black primary wedges so that, in flight, Ring-billed’s pattern looks surprisingly similar to that of Herring Gull; very white underwings reinforce this impression.
Second-years Similar to adult, but easily aged by the presence of dark feathering on the primary coverts. Most also show vestigial black markings on the tail and, sometimes, the secondaries (although many lack them). Conversely, some second-year Commons also show them (but usually only on the tertials). Ring-billed shows only a small white mirror on the inner web of the outer primary (often difficult to see), whereas second-year Common shows one or two obvious white mirrors. The age at which Ring-billed develops adult bare-part colouring varies: most acquire a complete black bill band and a yellow base by their first summer, although some still retain a black tip and/or a greenish base a year later; and some remain dark-eyed into their second summer.
First-years The most difficult age to identify, as many of the subtle differences are inconsistent. First-year Ring-billed has a distinctive ‘jizz’ once learnt, but it should always be identified by a combination of minor differences. Close views and detailed notes or photographs are essential, and observers should always bear in mind the possible occurrence of odd Common Gulls (for example, unusually pale individuals). All the following features (in rough order of significance) should be checked. 1 BILL The best character, being heavy, thick, ‘parallel’ and blunt-ended (Common’s bill looks slender, pointed and weedy). Usually pale orangey-pink with a prominent black tip, strangely reminiscent of the bill of first-winter Glaucous Gull L. hyperboreus (some Commons have a similar bill colour, but most have a duller, grey or greenish base). 2 TERTIALS Solidly dark brown, narrowly fringed white (on Common, paler brown, with broad white fringes, but beware the effects of abrasion). 3 MANTLE AND SCAPULARS Pale grey, lacking the dark ‘saddle’ effect of Common. Whitish tips to many of the scapulars and the retention of some dark juvenile feathering may create a more variegated pattern than Common, but the dark feathers are moulted and pale tips wear off as winter progresses. 4 GREATER COVERTS Usually appear pale grey, sometimes barred on the inners (unlike Common), producing a pale strip along the base of the closed wing and forming a noticeable pale mid-wing panel in flight. 5 HEAD AND UNDERPARTS Usually well mottled and spotted about the head (first-winters with head streaking may show a white eye-ringed effect) and more heavily mottled or scalloped below. There is often heavy dark barring or spotting on both the upper- and undertail-coverts, which Common usually lacks. Both species, however, are variable. 6 TAIL The dark of the tail-band usually extends up the outer web of each tail feather to intrude into the tail base, which usually shows delicate greyish mottling or shading (occasionally almost an all-dark tail); the tail therefore looks messy compared to Common, which shows a clear-cut band and a white base. On some Commons, however, dark also intrudes into the white, while a minority also show grey mottling at the base, so the difference is not absolute. Ring-billed has dark mottling or barring on the outer web of the outer tail feather, which Common seems to lack. 7 MEDIAN COVERTS In fresh plumage, the brown centres to the median coverts are pointed on Ring-billed, rounded on Common, but this distinction breaks down with wear and fading, and is of little use in worn plumage. 8 LEGS Sometimes quite pink on first-year Ring-billed (but may be pale greyish).
First-summer Both species fade and bleach, and eventually replace their wing-coverts and tertials with grey second-winter plumage. First-summer Commons look washed-out and pale, their outer primaries and secondaries fading to brown and the rest of the wing becoming creamy and worn, contrasting conspicuously with the dark grey ‘saddle’, particularly in flight. Ring-billed also fades but, because it lacks the dark ‘saddle’, the mantle and wing-coverts look uniformly pale grey and concolorous. Unlike Common, first-year Ring-billed soon gains a pale bill tip and, by their first summer, the bill pattern is usually similar to that of the adult.
Juveniles Full juvenile has never been recorded in Britain and Ireland. Similar to first-winter, but mantle and scapulars brown, fringed white, and the head and underparts are also heavily marked.
First-year and second-year Ring-billed may be confused with second- and third-year Herring Gulls respectively, both of which can show a prominent bill band. The easiest and most obvious difference is their size: most Herring should appear large, bulky, angular-headed, heavy-billed and meaner-looking. If in doubt, check the wing-coverts: second-year Herring shows noticeable brown barring across the wing-coverts (including the greater coverts), which first-year Ring-billed lacks; in addition, second-year Herring shows rather mottled tertials and, usually, a pale eye. In flight, second-year Herring shows fairly uniform grey inner primaries, producing a pale grey ‘window’ extending to the tips of the feathers; first-year Ring-billed has dark subterminal marks on these feathers. Third-year Herring is also easily separated as it retains traces of dark mottling on the wing-coverts, obvious vestiges of immaturity that second-year Ring-billed would never exhibit (although small amounts of brown may be retained on the leading lesser coverts); third-year Herring also has pinkish legs, whereas second-year Ring-billed usually has greenish or yellowish legs.
General approach Many birders find the identification of large gulls daunting. The best approach is to familiarise yourself with the Herring Gull, which should act as the yardstick. Start with adults, gradually moving on to third- and second-years, before looking at juveniles and first-years. The first real identification challenge is the separation of juvenile and first-year Herring Gulls from similarly aged Lesser Black-backed Gulls.
Ageing immature large gulls – general principles Aside from hybridisation, the reason why immature large gulls are so difficult to identify is related to three main factors: (1) moult, (2) individual variation and (3) the effects of wear and bleaching.
Moults Juvenile A large gull’s first plumage is ‘juvenile’. This is brown, heavily patterned on the upperparts and always neat and immaculate. The mantle and scapulars have brown feathers with white fringes, forming a scalloped appearance. First-year In late summer and autumn, most juveniles begin moulting into first-winter plumage. This involves just the back and scapulars, and variable numbers of head and body feathers. The back and scapulars then show anchor-shaped marks and/or cross-barring. In their first-summer, many species acquire extensive but variable amounts of greyer second-winter feathering on their back and scapulars (the shade depending on the species) while simultaneously their old juvenile or first-winter feathers become very worn and often bleached (the new greyer feathers help considerably in the identification process). Strictly speaking, however, ‘first-summer’ is not a discrete plumage, but simply the early stages of the bird’s moult into second-winter . Second-year The sequence in their second-year is similar to the first, gradually acquiring more adult-like grey feathering on their back and scapulars by their second-summer, and later the wing-coverts. Second-years otherwise retain extensive black in their primaries, primary coverts, secondaries and tail. Third-year Third-winter plumage is similar to adult, but variable amounts of brown immature feathering remain (particularly on the wing-coverts, primary coverts and tail), but this becomes increasingly limited; the bare parts may also retain signs of immaturity. Owing to their relatively consistent appearance, third-years are not usually covered in the individual species accounts below. Fourth-year Although essentially adult, many retain subtle traces of immaturity (as indeed can a few even older individuals).
Useful tips 1. Shape of juvenile primary tips A useful point to remember is that both juvenile and first-year large gulls have slightly more pointed primary tips than older birds and, when worn, these are often obviously pointed, contrasting with any newly growing, rounded, second-year feathers. This may help to age puzzling individuals.
2. Effect of moult timing on subsequent plumage type The earlier an immature gull moults, the more ‘immature-like’ the replacement feathers will be; the later it moults, the more ‘adult-like’ they will be. Thus, a first-year gull moulting in May will replace the old feathers with more immature-like feathers than a gull replacing those same feathers in August, which will grow more adult-like feathers. This explains much of the individual variation (and is presumably related to hormone levels).
3. Effect of latitude on moult timing Southerly species breed earlier than northern ones and they subsequently moult earlier; consequently, they are usually more advanced in their moults and in their acquisition of the next age of feathering. Thus, Yellow-legged and Caspian Gulls acquire significant amounts of plain grey adult-like feathers in their first-summer, whereas ‘first-summer’ Herrings, Lesser Black-backs and Great Black-backs do not. This is significant for identification.
4. Variation As indicated above, the plumage of large gulls is extremely variable and some defy accurate ageing. For example, colour ringing has revealed that a few second-winter Herring Gulls look just like third-winters.
Aberrant birds and hybrids If a gull doesn’t look right, check for anomalous features – both plumage and structural – that may suggest aberration (albinism, leucism, etc.) or hybridisation. There are no easy answers to this, except logical thought and an open mind. Olsen & Larsson (2003) and Howell & Dunn (2007) are recommended for further reading.
Where and when Herring Gull – the familiar ‘seagull’ of seaside towns – is a common breeding bird around our coasts and also inland on city buildings. It is more widespread in winter, when Scandinavian immigrants of the nominate race argentatus are numerous in some northern and eastern areas.
Size and structure Generally slightly larger and stockier than Lesser Black-back, with a shorter, less attenuated rear end at rest. Being a more sedentary species, the wings are proportionately slightly broader, shorter and less pointed in flight, and the body appears slightly bulkier.
Plumage Adult Easily identified by its pale grey mantle, black wing-tips and pale pink legs (note that the black in the wing-tips may become severely reduced during autumn primary moult, when the wings are much more rounded). Beware of confusion with the much smaller Common Gull (see p.207). Juvenile Similar to juvenile Lesser Black-back (see Lesser Black-backed Gull Larus fuscus) but plumage is slightly but distinctly paler, being more grey-brown, less smoky looking. The feather fringes are also generally paler. At rest, the most important differences are: 1 TERTIALS Herrings show obvious whitish notching around the fringes and tip (although there is individual variation in the exact pattern). 2 GREATER COVERTS Obviously chequered, normally lacking the thick dark bar across the inner greater coverts of most Lessers (at the base of the closed wing, nearest the wing bend). 3 HEAD Subtly paler, plainer and more bland-looking than Lesser Black-back. 4 IN FLIGHT Usually appears paler with the following differences from Lesser: (1) more obvious whitish inner primary ‘windows’, both above and below (the latter obviously translucent against the light); (2) paler brown underwing-coverts (not dark chocolate-brown), making the underwing appear paler and more uniform and (3) a slightly narrower tail-band with more white at the base; also, the tail-band does not contrast as strongly with the uppertail-coverts and rump, which are not as white looking as Lesser, being more heavily mottled. The structural differences outlined above are also useful. First-winter By late August/September, a partial post-juvenile body moult gradually introduces new mantle and scapulars feathers, which have brown anchor-shaped markings or more distinct cross-barring; when fresh, these feathers have a buff background, which soon whitens. The head and underparts also become whiter as winter progresses. First-summer Unlike Lesser Black-back and Yellow-legged, most show little if any adult-like pale grey feathering on the back and scapulars (if present, it is usually confined to a limited area on the upper back). Instead, any new feathers resemble first-winter and, as these are mixed with old, worn, first-winter feathering, individuals in active moult often look very scruffy. Note that, on the scapulars, the new feathers may be heavily barred dark brown on a whitish background. New second-winter tertials may show extensive white at the tips. The head and underparts may also retain scruffy grey streaking and mottling. By late summer, however, a minority show extensive pale grey on the back and scapulars, but these feathers usually have brown shaft-streaks and limited cross-barring. Second-year Very variable. At first surprisingly similar to first-year, with extensively scalloped or barred upperparts (but new brown tertials and greater coverts are often lightly peppered with white). Pale grey feathering gradually appears on the back and scapulars, and usually dominates by midwinter, providing an obvious difference from similarly aged Lessers. The underwings remain paler brown than equivalent Lessers, some being quite white. They gradually acquire a pale eye and an extensive pale base to the bill. If in doubt about ageing, the shape of the primary tips may be useful.
Herring Gulls breeding in Britain and Ireland are of the race argenteus. In Scandinavia, nominate argentatus takes over, becoming larger and darker towards the north, with less black in the primaries. In many parts of n. and e. Britain, most winter Herring Gulls are of Scandinavian origin. Whilst many are not safely separable in the field from argenteus, the more extreme examples are markedly different (see below). The more distinctive adults (apparently from N. Norway and the White Sea) have a darker mantle, which also tends to be colder grey. Such birds generally show reduced black in the wing-tip, large white tips to the outer two primaries, larger white primary spots at rest and a broader white tertial crescent (see pp. 230, 231 and Pitfalls). In flight, some of these dark birds are predominantly white on the underwing, often showing little black on the under-primaries. In addition, they tend to show a very heavy and angular head, heavy neck streaking in winter, a large, pale, washed-out bill and a particularly ‘mean’ expression. They also tend to be bulkier and have a pronounced tertial step. A few Baltic argentatus (formerly known as ‘ omissus’) have yellow legs, perhaps birds with Yellow-legged or Caspian Gulls in their ancestry. Immatures Some, presumably more northern juvenile/first-winters, may appear rather large, with paler plumage than argenteus (almost suggesting juvenile Glaucous L. hyperboreus or Iceland Gulls L. glaucoides). More distinctive individuals have obviously pale brown primaries with noticeable creamy-white fringes to the individual feathers.
It is possible that some such birds have Glaucous Gull in their ancestry and apparent first-generation Herring × Glaucous Gull hybrids have been seen in Britain (often called ‘Nelson’s Gull’ in North America). Smaller individuals may also suggest Thayer’s Gull (see Thayer’s Gull L. g. thayeri).
Where and when Breeds around much of the British and Irish coast (rarer on English east coast) and nests abundantly on buildings in many inland cities. Also widespread in winter (rarer in n. Scotland) with most inland, often on farmland. Lesser Black-back is strongly migratory and many head south to winter on coasts of Iberia and NW Africa (some reaching W. Africa). The darker Scandinavian race intermedius also occurs in small numbers, mainly in winter. The Baltic race fuscus – or ‘Baltic Gull’ – is on the British List by virtue of two recoveries ringed as chicks in Finland. Given that it migrates south or south-east to winter on the coasts of E. Africa, it is a relatively unlikely vagrant to Britain. However, a number of recent well-documented claims suggest that small numbers do occur, but the Rarities Committee will currently accept only records of birds ringed within the breeding range (Kehoe 2006).
Size and structure Similar size to Herring Gull, but marginally smaller and slighter, with a slightly smaller bill. Being a longer-range migrant, it has long wings, so at rest Lesser looks ‘long and low’ with long pointed primaries and a tapered rear end. These structural differences are particularly useful in flight, especially when identifying first-years or birds high overhead: compared to Herring, Lesser Black-back looks slim, with proportionately longer, narrower and more pointed wings.
Calls Adult’s calls are distinctly deeper than those of Herring Gull.
Plumage Adult British race graellsii For differences from Great Black-backed Gull, see Great Black-backed Gull Larus marinus. 1 UPPERPARTS Very dark blackish-grey above, obviously paler than Great Black-back. In winter, the head and neck show heavy grey streaking, but a pre-breeding body moult from January onwards soon produces a white head. 2 UNDERWINGS Viewed from below, has dark grey across the inner primaries and secondaries (Herring is completely and obviously white in this area). 3 BARE PARTS Legs bright yellow in summer but dull creamy-yellow in winter (pale pink on Herring). In summer, the bill is often brighter than Herring’s and the orbital-ring is red (orange or orange-yellow on Herring). Juvenile 1 UPPERPARTS Compared to juvenile Herring Gulls, juvenile Lessers are distinctly dark and rather smoky looking, both above and below. The back, scapulars and wing-coverts appear rather chocolate-brown, the individual feathers being less contrastingly fringed grey-buff or dark buff. The dark tertials are relatively plain with a narrow whitish fringe, lacking the obvious notching of Herring Gull; however, many Lessers show slight notching, particularly towards the tip, while a minority show stronger whitish indentations at the tip, more similar to many Yellow-legged Gulls. Unlike Herring, at rest most juvenile Lessers show a variable thick dark bar across the bases of the inner greater coverts (i.e. those closest to the bend of the wing), this being similar to that shown by juvenile Yellow-legged Gull. 2 IN FLIGHT If in doubt, juvenile Lessers are more easily identified in flight. The dark, smoky appearance is obvious, the wing-coverts contrasting much less strongly with the black primaries and secondaries. Most importantly, unlike Herring and Yellow-legged, on juvenile Lesser’s upperwing the black of the secondaries extends right across the inner primaries, forming a solidly dark rear wing (with a narrow white trailing edge), lacking the obvious pale inner primary windows shown by Herring and, to a lesser extent, Yellow-legged Gull (Lesser shows only subdued greyish-white windows). The underwing too is dark, with chocolate-brown underwing-coverts that show relatively little contrast with the dark grey or black flight feathers. Lesser may show more black on the tail, covering all but the base; in flight this contrasts more strongly with the white rump and uppertail-coverts, which are less mottled than Herring. 3 AUTUMN JUVENILES Note that juvenile Lessers often fade considerably by early autumn, the browns becoming paler and the feather fringes and background colour to the head and underparts becoming white. Such birds may then suggest Herring Gull or, more particularly, Yellow-legged and even Caspian Gulls; nevertheless they can be separated by most of the features outlined above. First-winter By late August and September, juveniles usually begin a variable and partial body moult into first-winter plumage. They gradually acquire new feathers on the back and scapulars, showing a distinct anchor-shaped pattern; the head and underparts continue to whiten. Dark chocolate underwing-coverts are retained (paler brown on Herring). First-summer Acquired from early spring onwards. Incredibly variable, but most look quite dark as a result of the gradual acquisition of second-winter feathering, which has a dark grey background colour (albeit with variable dark chocolate-brown shaft-streaks, anchors, cross-bars and often pale fringes). Other feathers gained at this time are more like first-winter, being dark chocolate, variably patterned with darker brown. In active moult, the mix of new second-winter feathers and old worn first-winter feathers creates an extremely scruffy appearance (many old feathers become severely bleached, especially across the wing-coverts and tertials). Significantly, first-summer Herring Gulls acquire little, if any, adult-like pale grey back and scapular feathers and so remain much as first-winter, appearing paler and browner than Lessers, but often strongly barred brown across the whitish scapulars (once the new second-winter feathering is acquired). Second-year Very variable, the result of a complicated mixture of adult-like dark grey and immature-like pale chocolate feathering (both feather types variably patterned with dark brown and sometimes fringed paler). While some have extensive plain, adult-like dark grey feathering on the back and scapulars, a minority remain more like first-winters, being heavily patterned with dark anchors, diamonds and cross-bars on quite a pale background. Nevertheless, all are distinctly darker above than second-winter Herring Gulls. The tertials show more extensive white at the tip, often with a large anchor shape within the white. The eye gradually turns pale, as does the bill base. In flight, the underwing-coverts remain dark chocolate-brown. By their second-summer, the mantle and scapulars become predominantly dark grey, forming a distinct ‘saddle’, and many also show extensive dark grey on the upperwing-coverts, increasing considerably by late summer. The head and underparts become white and the bare parts often brighten considerably.
Scandinavian races
Adult intermedius Lesser Black-backs become darker towards the north and east. As its name suggests, Scandinavian intermedius is intermediate in shade between British graellsii and nominate Baltic fuscus, appearing distinctly darker and blacker than graellsii. Both its structure and the timing of its moults are similar to graellsii.
Adult fuscus Classic individuals are distinctly or even strikingly smaller and slighter than graellsii, with a smaller, slimmer bill, more domed head, shorter legs and long, scissor-like primaries (it has long slender wings in flight). Their jizz may be reminiscent of a smaller gull, such as Common Gull L. canus. The upperparts are virtually black, similar in shade to Great Black-back, showing little contrast with the black primaries, which have only a small white mirror on the inner web of the outer primary. Fuscus also has a whiter head in winter, with light grey streaking confined to the crown and hindneck.
Moult Differences are particularly significant: graellsii and intermedius have a complete post-breeding moult from mid May to December, with their primary moult commencing anytime between May and August. Apart from perhaps the innermost one or two primaries, fuscus does not commence its primary moult until arrival in its winter quarters, from October to April. Consequently, any late summer/autumn fuscus seen in Britain is likely to have old and worn primaries until at least October, by which time local graellsii will have new, fresh primaries. Winter fuscus should be in active primary moult, whilst in spring the primaries should be new and fresh at a time when graellsii’s are starting to wear. However, great caution must be taken when identifying a potential fuscus in Britain. In particular, the effects of the light must be carefully considered, particularly at evening roosts (in certain lights even graellsii can look very dark). There is also intergradation between fuscus and intermedius while, apparently, some small female intermedius closely resemble fuscus. It has to be accepted that any apparent fuscus seen in Britain is unlikely to make it beyond the level of ‘possible’ or ‘probable’, unless of course it carries an identifiable ring.
Where and when Breeds fairly commonly, mainly on rocky coastlines, right around Britain and Ireland, except along the British east coast south of the Firth of Forth. More widespread in winter, when Norwegian immigrants are common in the east, penetrating well inland. Small numbers of local breeders may also feed throughout the year on inland lakes and reservoirs.
Size and structure Fundamental to its identification. A huge, bulky brute of a gull, with a large head, deep chest, often a pronounced tertial step and a somewhat truncated rear end. Conspicuously larger than all other gulls and always dominates them when feeding. Males are larger than females, but most are c. 20% larger than Lesser Black-back and, more importantly, about twice as heavy. In comparison, Lesser is rather slender, with long primaries that at rest produce an obviously tapered look to the rear end (but wings appear shorter during autumn primary moult). Great Black-back’s deep and powerful bill is always conspicuously larger than that of Lesser Black-backed and Herring Gulls, with a rather bulbous tip and prominent gonydeal angle. Note also the small beady eye (looks dark at any distance), set well back on the head. In flight, it appears slow, lumbering and pregnant-looking, with relatively rounded wings and slow wingbeats (its 1.5m wingspan is larger than that of Common Buzzard Buteo buteo) . In comparison, Lesser Black-backed’s wings are long, narrow and pointed although, in the absence of direct comparison, Great Black-backed’s can look proportionately somewhat shorter.
Calls Adults’ somewhat muffled calls are loud, deep, powerful and often bellowing.
Plumage Adult If seen well, separation from Lesser Black-backed is not difficult but, if accurate size assessment is not possible, confusion is surprisingly easy, especially if poor light affects the mantle colour. 1 UPPERPARTS Great Black-back is virtually black above, readily separating it from the British race graellsii of Lesser Black-back (Scandinavian Lesser Black-backs – intermedius and the rare fuscus – are darker above). At rest, Great Black-back has a thicker and more prominent white tertial crescent. 2 LEG COLOUR When in doubt, concentrate on size, structure and leg colour, Great Black-back having flesh-coloured legs (Lesser Black-back yellow, bright in summer but duller in winter when the yellow can be difficult to discern in weak light). 3 HEAD COLOUR IN WINTER Great Black-back retains a largely white head in winter (any markings are faint) whereas graellsii Lesser has a heavily streaked head until at least December. 4 IN FLIGHT Great Black-back is blackish right across the wings, whereas the paler wings of graellsii Lesser contrast with the blacker primaries. Great Black-back has large white tips to the outer two primaries forming a diagnostic and conspicuous white spot at the wing-tip (Lesser usually has much less obvious subterminal mirrors). Greater also has a broader white trailing edge to the wing that contrasts much more strongly with the blackish upperwings. The under-primaries and under-secondaries are noticeably dark grey. Juvenile Most likely to be confused with similarly aged Herring Gulls (and even more similar to juvenile Yellow-legged Gull, which see), so correct size and structural evaluation is essential. 1 BILL Pay particular attention to the large black bill, which usually contrasts strongly with the predominantly white head (lightly streaked around and behind the eye). 2 UPPERPARTS Plumage neat and immaculate and appears much ‘cleaner’ than first-year Herring, with a buffy-white background colour (gradually wearing whiter). The wing-coverts are distinctly chequered with chocolate-brown, whereas the mantle and scapulars are plain brown, each feather neatly fringed with white (Herring’s underparts and upperparts are browner, the latter with a less contrasting, duller ground colour, but some pale individuals can look more similar to Great Black-back). The tertials show broad white tips and fringes. 3 IN FLIGHT The rather pale upperwing-coverts contrast quite strongly with the black primaries and secondaries. Most useful in flight is a rather narrow tail-band which, at close range, often has a series of narrow black bars in front of it and thus appears ill-defined (tail-band solidly brown or black on Herring and Yellow-legged Gulls). Unlike Herring, the tail-band contrasts strongly with the white base, uppertail-coverts and rump, which are only lightly mottled. First-year 1 UPPERPARTS Following partial post-juvenile body moult in autumn, the head and underparts become even whiter and the white-fringed juvenile mantle and scapular feathers are gradually replaced by first-winter feathers that show brown anchor-shaped marks on a buff background, with noticeable white fringes (producing a more barred impression). 2 BILL Black throughout the first winter, but often acquires a pale tip and base in the first summer (Herring usually acquires a paler base during its first winter). Second-year 1 PLUMAGE Becomes even whiter on head and underparts. Initially very heavily patterned above, often with obviously all-dark greater coverts. It gradually acquires obvious blackish feathering on the back and scapulars, allowing easy identification. 2 BILL Becomes paler and pinker, with black only at the tip, and the eye gradually turns pale.
References Olsen & Larsson (2003), Howell & Dunn (2007).
Background Some of the greatest recent advances in bird identification have related to the large gulls. It has always been known that the widespread and familiar ‘Herring Gull’ occurs in various forms across the Northern Hemisphere, but recent developments in the analysis of their DNA have indicated that, what was formerly considered one species, is at least six. These can be divided into two clades (groups of closely related species that share a common ancestry). The North Atlantic clade contains European Herring Gull, Yellow-legged Gull and Armenian Gull L. armenicus as well as Great Black-backed Gull L. marinus, all evolving from a common ancestor in the North Atlantic. The Aralo-Caspian clade (named after the Aral and Caspian Seas in SW Asia, a past hub of gull evolution) contains Caspian Gull, all races of Lesser Black-backed Gull L. fuscus, the various Siberian forms of ‘Herring Gull’ and, remarkably, American Herring Gull L. smithsonianus, the ancestors of which apparently colonised North America not from the Atlantic, but from Asia. As far as we in Britain are concerned, the most significant changes relate to Yellow-legged and Caspian Gulls. It has long been known that the former is a regular late summer and winter visitor from the Mediterranean, and the Atlantic coasts of Iberia and France. Caspian Gull, which breeds principally in SE Europe and SW Asia, was officially split as recently as 2008. In recent years it has started to spread north-west and is now breeding as close as Poland. The problem is that, as with many expanding species, the pioneers are interbreeding with a closely related species, in this case Herring Gull. Although classic Caspian Gulls are fairly distinctive, it is this hybridisation that makes it such a difficult and controversial species to identify.
Where and when Most occur in late summer (July to September) with smaller numbers remaining until late winter (by spring and early summer, only a few immatures usually remain). They occur both on the coast and inland, particularly on rubbish tips and reservoirs. Since 1995, one or two pairs have bred in s. England.
Size and structure Older birds are usually located by their darker grey mantle (see below) but structural differences are also significant. Somewhat larger and more powerful than Herring Gull and males may be particularly big, clearly intermediate in size between Herring and Great Black-back. The bill is usually longer, heavier and more bulbous than Herring’s, with a deep and rather blunt tip; some large males have a particularly long and heavy bill. It also tends to be deeper-breasted and rather long-legged, sometimes producing a distinctly gangly impression (often adopts a very horizontal stance with a bulbous breast and long legs). In flight, it has noticeably long, pointed wings and glides on arched wings, rather like a skua. Those that occur in Britain are of the w. Mediterranean race michahellis, but some resemble so-called ‘ lusitanius’ from w. Iberia (see ‘Lusitanius’ Yellow-legged Gulls).
Plumage A useful point to remember is that, as they breed further south, Yellow-legged Gulls nest earlier than both Herring and Lesser Black-backed; consequently, at each plumage stage young birds mature significantly earlier than equivalent-aged Herring Gulls.
Adult Superficially similar to Herring Gull, but remember that it shares many features with Lesser Black-back. When separating adults, the following should be looked for (in approximate order of significance): 1 MANTLE Clearly a darker ‘mid grey’, intermediate between graellsii Lesser Black-back and argenteus Herring (similar, in fact, to Common Gull L. canus, but warmer). 2 LEGS Yellow, bright in summer, but paler and washed-out in winter (when the colour can be difficult to determine). 3 HEAD SHAPE At rest looks bulbous with a thick neck but, when alert, may show a rather small, flat head and distinctly long neck. 4 HEAD STREAKING Lacks Herring Gull’s heavy head streaking in winter, instead showing only limited light grey streaking in autumn and early winter on the crown, perhaps on the nape and most obviously a stronger backward-pointed area around and behind the eye. This difference is valid only until late December/January onwards when both Yellow-legged and argenteus Herrings start to acquire their white summer head colour. However, early moulting Yellow-leggeds often stand out as sleek, smart and contrasting amongst winter-plumaged Herrings. 5 BILL Brightly coloured with a large red spot; it may acquire a narrow black band in winter. 6 ORBITAL-RING Red, like Lesser Black-back, producing a beady-eyed effect at a distance (yellow or orangey-yellow on Herring). 7 UPPERWING In flight, tips more extensively black than Herring; also, the black wing-tips are cut off more squarely and show little white at the tip (two mirrors on P9 and P10). 8 UNDERWING Dusky-grey across the under-secondaries and inner primaries (not as dark as Lesser Black-back); Herring is all white in this region. 9 MOULT Earlier than Herring, with extensive primary moult from July to early September. Primaries are practically fully grown by September, when local argenteus Herring’s are usually still short and partially grown. 10 CALLS Distinctly louder and deeper than those of Herring Gull (and Lesser Black-back), often recalling Great Black-back.
Juvenile Superficially similar to juvenile Herring Gull, both at rest and in flight, but it has a distinctly white background colour, creating a smarter, cleaner impression. In consequence, Yellow-legged is oddly reminiscent of juvenile Great Black-back, being rather white-headed with rather pale, ‘clean’-looking mid brown upperparts with contrasting whitish feather fringes (forming a strong contrast with the very dark tertials, primaries and secondaries). Note that juvenile Lesser Black-backs, although they start off dark, often fade considerably by early autumn, with paler brown plumage, a pure white background colour to the head and underparts, and white feather fringes to the upperparts; such birds can strongly suggest Yellow-legged. Concentrate on the following. 1 HEAD The head and neck pattern can be divided into three areas. (1) There is fine grey streaking on the crown and a large greyish smudge or ‘shadow’ that extends behind and below the eye to form an ill-defined but fairly noticeable mask. (2) Immediately behind this area is a large crescent-shaped swathe of white, running from the upper nape down the neck-sides, below the eye shadow. (3) Below this again, the hind-neck is strongly streaked brown, forming a ‘shawl’ that runs onto the lower neck-sides and to the upper breast, the streaking then extending onto the breast and belly. The ground colour to this whole area is very white, contributing to the very clean impression. 2 UPPERPARTS At rest, juveniles are mid brown, with nearly all the feathers showing contrasting buffish-white fringes that produce a clean-cut, well-patterned, scalloped appearance (little chequering, most obvious on the inner greater coverts). A useful aide-mémoire is that the combination of white-looking head, dark eye shadow and whitish-fringed upperpart feathering can, with some imagination, suggest a giant juvenile Mediterranean Gull L. melanocephalus. 3 GREATER COVERTS Also distinctive is that, like Lesser Black-back (but unlike Herring) most Yellow-leggeds show dark bases to the outer greater coverts, forming a thick dark band across the lower edge of the closed wing (closest to the wing bend), but note that this area may be hidden by the fluffed-up flank feathers. 4 TERTIALS Unlike Herring (which shows strong notching) the tertials are plain brown with white feather fringes (similar to Lesser Black-back). Many also show white indentations at the tips (the so-called ‘oak leaf’ effect), while others show a thick dark anchor at the tip with deep white indentations behind (then a solidly dark basal area). 5 IN FLIGHT Juvenile Yellow-legged shows a relatively narrow but clear-cut jet back tail-band (usually slightly browner on Herring) that contrasts strongly with the pure white base, rump and uppertail-coverts, all of which show only limited black mottling. The very dark secondary bar contrasts quite strongly with the pale wing-coverts and most show a second dark bar across the outer greater coverts, in front of the secondary bar (but this can be surprisingly difficult to confirm on the moving wing). Although it shows a pale ‘window’ on the inner primaries, this is much less obvious than on Herring Gull. Although somewhat variable, the underwing-coverts often stand out as rather dark chocolate-brown (like Lesser Black-back) contrasting with the predominantly greyish flight feathers (underwing paler and more uniformly brown on Herring). When flying head-on, it shows two prominent buff ‘landing lights’ at the bend of each wing, much more obvious than the equivalent marks on Herring and Lesser Black-back. To eliminate Great Black-back, remember that this species has an obviously narrow tail-band that is often broken into rows of thin black bars, creating an ill-defined and rather messy pattern at a distance. Notwithstanding large male Yellow-leggeds, Great Black-back should always look considerably larger and more powerful, with an extremely large and heavy-ended bill.
First-winter By late July, some start to acquire first-winter feathers on the back and scapulars, these being buff with blackish anchor-shaped markings and basal cross-bars, these predominating by early autumn.
First-summer Unlike Herring and Lesser Black-backs, most first-summer Yellow-leggeds acquire extensive plain grey second-winter feathering on the back and scapulars, often appearing very clean-cut and contrasting. This may appear from early spring and predominates by late spring and summer, allowing such birds to be readily separated from Herring (which largely retains worn first-winter plumage) and Lesser Black-backed (which shows either new strongly patterned chocolate feathers on the back and scapulars or plain dark grey ones). Like the adults, Yellow-legged’s new feathers are a dark ‘mid grey’ so, as they mature, they become increasingly easy to pick out and identify. First-summers are also very white on the head and underparts but may still retain a darker shadow around the eye and an obvious shawl of heavy streaking around the hind neck. The tertials at this time often appear solidly brown, the whitish fringes having worn off. In flight, the underwing-coverts remain dark. The legs may turn yellowish.
Second-year Still shows dark primaries, secondary bar, tertials and tail-band, and also a dark band across the outer greater coverts. However, the extensive but variable ‘mid-grey’ that appears in their first-summer often spreads onto the wing-coverts and such birds appear much more advanced than similarly aged Herring Gulls. The shawl of dark streaking around the base of the hind-neck is often very obvious and the greyish eye shadow is often retained. The eye and bill base gradually turn pale (but variable). In flight, the underwing-coverts continue to show dark brown feathering. Following a spring body moult, the head, neck and underparts become pure white, the back and scapulars form a strong mid-grey ‘saddle’ and the wing-coverts are often strongly chequered (more advanced birds already have extensive grey in the wing-coverts). The bill often becomes bright yellow by late spring, with black and bright red at the tip. The legs also show a distinct yellow tone by midsummer.
Behaviour Less versatile in its feeding behaviour than Herring Gull. On the coast and at inland reservoirs, Yellow-leggeds often patrol quite high above the water (maybe 10–20m) and sometimes plunge for fish from low elevations (almost like a Gannet Morus bassanus). More usually, they scavenge, often hanging around behind a feeding Great Black-back, clearly taking second place in the pecking order ahead of Herrings and Lesser Black-backs. They also feed with other gulls on rubbish tips and in fields.
Pitfalls When identifying adult Yellow-legged Gulls, two particular pitfalls need to be considered. (1) Local argenteus Herrings can look dark in certain lights, a problem especially acute at evening gull roosts, and this can be compounded by the fact that argenteus regularly acquire a white head by January. (2) Confusion is also likely with Scandinavian Herring Gulls argentatus, which may be distinctly darker grey than local argenteus (see Scandinavian Herring Gulls L.a. argentatus, p.230, p.231 and Pitfalls). However, such birds tend to have less black and more white in the primaries and also show heavy winter head streaking.
Such hybrids are not infrequent and, inevitably, show a darker mantle than Herring Gull. However, the mantle tends to be a darker, ‘flatter’ shade of grey than Yellow-legged Gull. Also, unlike Yellow-legged, they show extensive head streaking in winter. Leg colour may be yellow but some show flesh-coloured legs, as well as a yellow or orangey orbital-ring (rather than Yellow-legged’s red). Such birds often appear very much halfway between the two species and fail to show Yellow-legged’s structural differences. If a potential Yellow-legged Gull does not look quite right, then consider a hybrid.
Some Yellow-legged Gulls seen in Britain resemble so-called ‘ lusitanius’ from w. Iberia. Such birds seem to occur mainly in south-western areas, usually from August onwards, often associating with Lesser Black-backs. They appear much more similar in shape to Lesser Black-back, being distinctly smaller than michahellis, with shorter legs, a distinctly short, thick-looking, rather stubby bill, a rounded head and a distinctly short thick neck.
There have been a number of British and Irish claims of gulls considered to be Azorean Gull . Winter adults resemble michahellis but are distinctive in that classic examples show a hood of dense dark grey streaking, whilst immatures appear very dark chocolate-brown. Any such bird should be carefully studied and photographed. For further information, see Olsen & Larson (2003) or check images on the internet.
Where and when Most occur in late autumn and winter in SE England, East Anglia and the East Midlands, with a few in the W. Midlands and NE England; rare elsewhere. They tend to frequent coastal areas, rubbish tips, pig fields and reservoir and gravel pit roosts.
General Caspian Gull has proved to be a difficult and controversial bird to identify, especially outside its normal areas of occurrence. The following attempts to strike a balance between clarity and the remorseless complexity that bedevils the subject. As a useful aide-mémoire, it may be helpful to think of Caspian as resembling a giant, long-billed, long-necked, beady-eyed Common Gull.
Size and structure Although similar to both Herring and Yellow-legged Gulls, its structure is likely to attract attention and is fundamental to its identification. 1 BILL When active, it usually shows a distinctly longer, slimmer bill than Herring Gull, with a weak gonydeal angle. It may also appear more pointed, a consequence of a gently curved tip to the upper mandible. However, females have shorter bills than males (overlapping with Herring Gull) and the bill of both sexes may be less striking when the bird is at rest, the fluffed-up head feathering reducing the impact of bill length. Beware also of Herring or other gulls showing an abnormally long bill (such aberrations are not infrequent). 2 STRUCTURE WHEN ACTIVE Similar in size to Herring Gull and, in direct comparison, males can appear quite big and bulky, females obviously smaller. It is a gentler looking, more elegant bird than Herring, with a flatter back, little or no tertial step and relatively long wings. The tail tip falls about one-third of the way along the closed primaries, compared with about halfway on Herring (but this feature is not valid with birds in outer primary moult). The head is small and rather pear-shaped, often showing a low, sloping forehead which, combined with the long bill, may give a drawn-out, ‘snouty’ impression. The neck is long and thin, producing a distinctive ‘wine bottle’ shape; the lower neck often shows an additional ‘bulge’ at the front, suggesting a bulging crop or an ‘Adam’s apple’. It also has a rather long and slightly decurved gape line. Distinctly longer spindly legs often give it a gangly impression. Its overall shape may be reminiscent of a giant Slender-billed Gull Chroicocephalus genei. 3 STRUCTURE AT REST When relaxed with its head sunk into its shoulders, its structure is far less distinctive. With the feathers fluffed-up, the head then looks more rounded, dome-shaped, or even square, but usually with a sloping forehead, an angle before the eye and an obviously rounded or slightly angular rear crown. The fluffed-up body plumage may also make the legs look shorter. It still has a distinctly deep-breasted impression and the underparts tend to show a distinct bulge in the ventral region, immediately behind the legs. At rest with its feathers sleeked (e.g. in hot weather) a combination of the long bill, pear-shaped head, high ‘bosomed’ breast, the ‘bulge’ in the ventral area and long wings is distinctive. This may be emphasised by its habit of standing with the body tipped at an angle, with the closed primaries pointing towards the ground. In flight, appears long-winged with a more protruding bill, head and neck.
Plumage Adult Likely to be located by a combination of structure, white head (even in winter), dark eye and ‘intermediate’ mantle colour. 1 HEAD In autumn and winter, looks noticeably white-headed, showing little if any streaking, which is fine and confined to a light dusting of pale grey on the crown or a more obvious ‘shadow’ around the eye, the latter emphasising a subtle white eye-ring. More distinctive is a shawl of fine pale grey streaking around the lower hindneck, but this usually wears off after autumn. 2 EYE Dark, standing out against the white head to give a softer, gentler demeanour than Herring Gull, although at a distance it can look ‘beady-eyed’ or ‘piggy-eyed’. At close range, the eye can often be seen to be ivory coloured. Beware of fourth-winter (or even adult) Herring and Yellow-legged Gulls with dark eyes. 3 BILL In winter, the bill is a rather dull, insipid, washed-out yellow, often tinged green, sometimes with small black spots or a narrow black ring crossing both mandibles, immediately behind the dull red gonydeal spot. In summer, the bill is bright yellow with a red gonydeal spot, lacking any dark. 4 LEGS Intermediate between Herring and Yellow-legged: an insipid greyish-pink in winter, often with a yellow tint (yellower in summer). 5 MANTLE COLOUR Paler than Yellow-legged and closer to argenteus Herring, being a quite a flat mid grey (also described as a neutral ‘silky’ grey) with less of a bluish hue than both races of Herring Gull (Gibbins et al. 2010), but bear in mind that the exact shade varies according to the light and angle of viewing. 6 PRIMARIES Having found a candidate, the most important feature on which to concentrate is the primaries. Firstly, these usually have two large white mirrors at the wing-tip: the larger (on P10) reaching the tip of the feather, the smaller on P9. More importantly, there is extensive pale in the primaries, which takes the form of long pale ‘tongues’ or ‘lobes’ on the inner webs (grey on the upperside, white on the underside). These are separated from the white at the tips by a relatively narrow band of black cutting across the entire width of the feather. This pattern of pale ‘tongues’ on the inner webs creates what is often referred to as a ‘Venetian Blind’ effect. This distinctive pattern is best evaluated on the underwing at rest, when the bird is preening, or if it droops its primaries. It is also apparent in flight, significantly reducing the size of the black in the primaries, particularly on the underwing (where the black hooks back along the trailing edge).
Juvenile 1 AT REST Very similar to juvenile Yellow-legged Gull (although rather more ‘washed-out’). Consequently, structure is fundamental to its identification at this age. Like Yellow-legged, it shows a subtle dark eye-patch, a curved area of white on the rear head/upper nape (extending onto the neck-sides) and a band of dark streaking on the hindneck (extending onto the upper breast). The mantle, scapulars and wing-coverts are ‘mouse-brown’ showing whitish fringes to all of the feathers, creating a scalloped impression. Like Yellow-legged and Lesser Black-backed (but unlike Herring) it has a thick dark bar across the outer greater coverts (at the base of the closed wing, closest to the wing bend). Chequering on the greater coverts is slight and, like Yellow-legged, is limited mainly to the inner feathers. It differs from Yellow-legged in showing broader, more diffuse white tips to the plain brown tertials, extending back around the outer edge of the feathers towards the base. The legs are a pale, washed-out flesh colour. Note that juvenile Lesser Black-backed Gulls, although starting off dark, often wear considerably by early autumn, with paler brown plumage and a pure white background colour to the head and underparts; they also show white feather fringes to the upperparts; such birds can suggest Caspian Gull – even their tertial pattern can be identical. 2 IN FLIGHT The most distinctive feature is that, unlike Herring and Yellow-legged, the underwing-coverts have a white background, but with grey-brown on the axillaries and narrow bands of grey-brown across the tips of the lesser and median coverts. It should be noted, however, that a minority of Caspian Gulls show more solidly dark lesser underwing-coverts. The under-primaries and secondaries are also paler (silvery to off-white). The pale inner primary window is usually somewhere between Herring and Yellow-legged in prominence, and is not a particularly helpful feature. As Yellow-legged Gull (and Lesser Black-back), in flight it shows a dark ‘bar’ across the greater coverts, immediately in front of the black secondary bar. Also like Yellow-legged Gull, the black tail-band contrasts strongly with the white tail base, uppertail-coverts and rump (thus showing more contrast than Herring Gull).
First-winter A post-juvenile body moult from mid August gives the bird a distinctive snow-white head, with only limited grey shading immediately around the eye (which largely fades away by winter). The white head forms a smart contrast with the largely all-black bill and also with a shawl of grey streaking around the lower hindneck. It also emphasises the dark eye. The underparts too become extremely white. The back and scapulars are rather pale grey with dark brown anchor-shaped marks; the important point about these markings is that they are very narrow, creating a much more delicate pattern than that shown by Herring and Yellow-legged (lacking the heavy anchors and strong cross-barring of Yellow-legged). The exact pattern of the scapulars is, however, variable, some showing delicate streaks, wedges, or diamond shapes (and occasionally somewhat heavier markings). The thick dark band across the outer greater coverts is retained (visible both at rest and in flight). The tertials are solidly dark with thick white tips. Most importantly, the underwings appear increasingly white (brown on Herring and dark brown on Yellow-legged).
First-summer Similar to first-winter but, as a result of wear and bleaching, generally paler and less contrasting. From late winter onwards, variable but often significant amounts of plain pale grey second-winter feathering appears on the back and scapulars. The bill base turns increasingly pale pink or yellowish, retaining a dark tip and cutting edges.
Second-year The complete moult that begins in spring or summer is completed by early autumn. Second-winter is similar to first-winter (including on some the shawl of grey streaking on the lower hindneck) but gradually acquires more extensive plain grey feathering on the back and scapulars (forming a grey saddle) and, later, the wing-coverts. Such birds are obviously ‘cleaner’ and greyer than similarly aged Herring Gulls, which retain extensive brown immature plumage. Some Caspians, however, appear much more similar to first-winter, with dark streaks, blobs or delicate anchors on the back and scapulars (but lacking strong anchors). The underwings become even whiter in second-year (but may retain limited brown markings). Unlike the more messily patterned Herring Gull, the black tail-band continues to contrast strongly with the white rump and uppertail-coverts. Most second-winter Caspians show a small white or off-white mirror in the outer primary (rare in Herring and Yellow-legged). The bill base continues to become paler and the legs grey-pink, but the eye remains dark (unlike most Herring and Yellow-legged Gulls).
Third-year In some ways third-years are more difficult to identify, as this age has few concrete plumage differences from Herring and Yellow-legged Gulls. Structure and general ‘jizz’ become the best ‘feature’, but note also the dark eye and the shawl of dark neck streaking. The bill is usually greenish-yellow with a black subterminal band. Differences in the primary pattern may be useful. Third-winter Caspians usually show large white mirrors on P9 and P10 (larger then equivalent Yellow-leggeds) but third-winter Herring can also show these. The following esoteric features are probably best analysed from photographs: (1) Caspian shows black bands across the tip of P5 (and often P4), which are rare on Herring, and (2) some also have the effect of grey ‘tongues’ on the inner webs of the middle primaries. Remember that some third-year Herring Gulls have dark eyes and white heads, and can look disconcertingly similar to Caspian (concentrate on structure).
Behaviour When feeding on water, they often duck their head in and even up-end, rather like Slender-billed Gull. Also when feeding, they often raise their wings, especially in aggressive interactions.
Calls and long-call posture The calls are surprisingly distinctive. The ‘long call’, begins with a deep, throaty eaah eaah or a deep, buzzing zeep zeep followed by a deep, rather fast, rhythmic laughing: ah-ah-ah-ah-ah-ah-ah-ah, oddly reminiscent of Common Guillemot Uria aalge. This is given with the head progressively raised and the wings held open and pushed back in a so-called ‘albatross posture’ (birds squabbling over food may indulge in this behaviour). The normal call is also distinctive: a peculiar deep, rather nasal, buzzing zeeeup.
Further reading For further information on the complicated identification of this species (and hybrids) see Gibbins et al. (2010, 2011).
References Gibbins et al. (2010, 2011).
Where and when Both are scarce winter visitors, mainly from October to May, but numbers vary considerably from year to year, with periodic influxes. They are liable to occur anywhere that attracts large gulls. Most of our Glaucous Gulls Larus hyperboreus originate from e. Greenland and Arctic Europe, so they tend to occur in the north-west, the north, and on the east coast. Despite their name, Iceland Gulls L. glaucoides originate from Greenland, so have more of a north-westerly distribution. The NE Canadian race of Iceland Gull, kumlieni or ‘Kumlien’s Gull’, breeds principally on Baffin Island and winters in Iceland and NE Canada, south to the Great Lakes. It has proved to be a regular visitor to Britain and Ireland, in small numbers. The breeding range of Kumlien’s is sandwiched between Iceland and Thayer’s Gull L. g. thayeri, which breeds across the Canadian Arctic, mainly to the west of Kumlien’s. Thayer’s is currently treated as a full species in North America, but in Britain it is regarded as a race of Iceland Gull. There are currently no accepted records of Thayer’s in Britain, although two very strong claims are under consideration (and several accepted records in Ireland).
Size and structure Both can be separated from Herring Gull L. argentatus† by their white primaries but, to differentiate between them, concentrate on size, structure, head and bill shape and, on juveniles, bill colour. Size varies sexually, males averaging larger than females, but Glaucous is usually (but not always) much larger than Herring, approaching Great Black-backed Gull L. marinus in size; Iceland is similar to or slightly smaller than Herring. Glaucous is a large, powerful, mean-looking brute, with a relatively short, blunt primary projection and often a prominent tertial step. Iceland is a rather stocky but gentler looking, less powerful gull, often lacking a tertial step and has long, tapered primaries that produce an attenuated rear end. A useful way of evaluating the difference in the primary projection is that, on Glaucous, the projection beyond the tail is the same as, or shorter than, the bill length, whereas, on Iceland, it is longer than the bill. Iceland has quite short legs that are often deep pink. A useful aide-mémoire is that, structurally, Iceland suggests a rather delicate Lesser Black-backed Gull L. fuscus, whereas Glaucous suggests a large Herring.
Head and bill Although overall size and shape may be the first clue to their identification, pay particular attention to head and bill shape. Glaucous has a long, thick, heavy, rather ‘parallel’ bill, longer and thicker than Herring’s, but (unlike Great Black-back) lacking a prominent gonydeal angle. Its prominence is complemented by a low forehead, a flat crown and a peaked rear crown, all of which reinforce a general impression of severity. Iceland’s bill is shorter, slimmer, stubbier and more pointed, being similar to, or slightly shorter than, that of Lesser Black-back; its steeper forehead and rounded head create a gentler expression, reminiscent of Common Gull L. canus. (However, head shape differences require cautious evaluation as both species can vary according to attitude.)
Flight Identification Glaucous is a large, heavy, ‘lumbering’ gull, with broad wings and a lazy flight that recalls Great Black-backed. Iceland is smaller, but has a rather stocky body and proportionately longer, narrower wings; its tail appears slightly, but distinctly shorter than Herring’s and slightly more wedge-shaped. Its flight tends to be more energetic than that of Glaucous.
Plumage Juveniles and first-years Note that, unlike our common large gulls, juveniles of both species show very little if any post-juvenile moult until late winter so, to all intents and purposes, they remain ‘juvenile’ until then. Both are essentially pale, biscuit-brown, intricately and delicately mottled and barred, but with whiter primaries. Plumage tone varies individually, but most become paler through wear and bleaching. Bill colour is diagnostic: Glaucous has a pink bill with a prominent, clear-cut ‘dipped-in-ink’ black tip. Iceland’s is usually black with a small, inconspicuous pale area at the base (the pale becomes more extensive as winter progresses) but the black tip is not clear-cut and extends back along the cutting edge so that, at any distance, the tip appears to merge with the pale base. Second-years Usually paler and less well patterned than first-years; they may look very creamy when worn. Grey feathering on the mantle and scapulars is gradually acquired, but some second-years show very little grey, if any. Again, plumage tone varies individually, so concentrate on bill and eye colour for accurate ageing. Most significantly, both species acquire pale irides during their second year. On Iceland, the bill base turns creamy, and the black tip becomes sharply defined so that is more similar to first-winter Glaucous but, unlike Glaucous, the black tends to protrude back along the cutting edge so that the tip is less clear-cut. Second-year Glaucous usually acquires a pale tip to the bill and, sometimes, a yellowish tint to the base. Third-years Both gain a grey mantle, scapulars and wing-coverts, and are much more adult-like, but retain traces of immaturity on the wings and tail. They show dark terminal or subterminal markings on a yellow bill, but Iceland may acquire a greenish or greyish tint to the base; bill colour may brighten towards spring. Adults Both are similar. Fourth-years may retain hints of immaturity, including small dark markings on the bill.
General approach Any apparent Iceland Gull should be checked for features indicative of Kumlien’s Gull. The basic difference from nominate Iceland is that adults show variable amounts of grey in the primary tips, while juveniles and other immatures show pale brown in both the primaries and tail. There is, however, much individual variation in immatures, to the point where pale Kumlien’s will be impossible to separate from slightly darker nominate Iceland. Before identifying this race, first establish beyond doubt that the bird concerned is an Iceland Gull, mainly by the structural characteristics outlined above.
Plumage Adult. Adult Kumlien’s shows grey in the outer primaries, usually along the outer webs and subterminally across the tips. At rest, this usually appears as grey along the lower edge of the closed primaries, with two or three grey chevrons towards the tip. Although fairly obvious at rest, this may be surprisingly difficult to see in flight. The shade and precise extent of the grey varies individually, some birds looking, or appearing to look, blackish. Juvenile Kumlien’s resembles nominate glaucoides Iceland except they show distinctly browner primaries and tail (sometimes also a browner secondary bar). The darkness and extent of the brown varies individually; on some paler birds the dark in the primaries and tail may be apparent only in flight. Older immatures are similarly dark in the primaries and tail.
Thayer’s shares Kumlien’s Gull’s ‘Iceland-like’ structure and jizz, but adult Thayer’s has black primaries and, superficially, appears much more similar to Herring Gull. Note, however, that adult Thayer’s has a heavily streaked hood and breast-band in winter, and short, deep pink legs. Similarly, juvenile and other immature plumages of Thayer’s are darker than nominate Iceland or Kumlien’s. They also have black or blackish primaries, with noticeable whitish chevron-shaped tips to the individual feathers, as well as a blackish tail-band and secondary bar. The problem is that there is a certain amount of intergradation between Kumlien’s and Thayer’s, to the point where intermediate and ‘non-classic’ individuals will not be identifiable to race. Thayer’s and darker Kumlien’s also have to be separated from Herring Gulls, particularly those northern argentatus that show reduced black in the primaries (see below). If you come across a potential Thayer’s, take photographs, seek expert advice and consult detailed literature, such as Olsen & Larsson (2003) and Howell & Dunn (2007). There are also large numbers of useful gull photographs on the internet.
The following pitfalls should be considered when identifying any of the above.
Glaucous × Herring hybrids
Occasionally seen in Britain and Ireland (in North America, often referred to as ‘Nelson’s Gull’), such birds may show characters intermediate between the two species, but others may be very similar to Glaucous, revealing their true identity by traces of black in the primary tips (adults) or traces of dark brown on the outer primaries, secondaries and tail (immatures).
Northern Herring Gulls
Adults Dark Scandinavian Herring Gulls of the nominate race argentatus are common winter visitors to n. and e. Britain. Some, probably from the extreme north, are large and dark and show little black in the wing-tips. In flight, the black may be very difficult to detect at any distance, while the underwings are almost entirely white, often with faint grey shading only at the primary tips. As they can approach Great Black-backed in size, distant birds can be misidentified as Glaucous; they are, however, much darker above (similar to or even darker than Common Gull) while on the water they show a pronounced tertial step, a broad white tertial crescent and black primaries with very large white mirrors and primary tips. Immatures It seems increasingly likely that the large, pale, ‘Glaucous-like’ immature Herring Gulls that occur occasionally in northern and eastern areas are these birds’ offspring. It may be difficult, however, to decide what is a Glaucous × Herring hybrid and what is an immature Northern Herring, but unless an immature gull shows obvious pro-Glaucous characters, such as a Glaucous-like bill, consider the possibility of Northern Herring Gull (see Herring Gull Larus argentatus). First-years seem to be fairly consistent in their appearance, being large (sometimes approaching Great Black-backed), heavy-billed with their shape being typical of argentatus Herring Gull (see Scandinavian Herring Gulls L.a. argentatus). However, they are very pale brown on a whitish background and the primaries are brown (much paler than first-winter argenteus) with white feather fringes and pale submarginal markings; the bill has a pronounced gonydeal angle and is mainly black. In flight, they resemble very pale and severely washed-out argenteus Herring Gulls.
Leucism Older field guides may state that second-year Glaucous and Iceland Gulls are completely white. This is not so: even very faded second-years usually retain a creamy look, and close inspection will reveal traces of delicate patterning on the wings and tail. A pure white gull will almost certainly be aberrant, and structure and bare-part colours provide the best clues to its identity. (Note: leucistic or albino Lesser Black-backs are closer to Iceland in shape than leucistic or albino Herrings.) Second- or even third-summer Glaucous and Iceland may look very white at a distance, but closer views should reveal a grey ‘saddle’ (mantle and scapulars) and the other features outlined above.
Moulting Herring Gulls In autumn, moulting adult Herrings may show severely reduced areas of black in the wing-tips, which appear noticeably rounded as a result of partially grown outer primaries. In flight or at distance, such birds may suggest Glaucous or Iceland. Fortunately, with local argenteus this phenomenon occurs prior to the main arrival of Glaucous and Iceland Gulls (but argentatus moults later, finishing in November–January).
†All references to Herring Gull are to British race argenteus, unless otherwise stated.
References Howell & Dunn (2007), Olsen & Larsson (2003).
Where and when Sandwich Tern Thalasseus sandvicensis is a common summer visitor, likely to be seen on coasts from March to October (very small numbers winter, mainly on the south coast); small parties may appear briefly inland on migration. Gull-billed Tern Gelochelidon nilotica is a very rare vagrant, currently averaging about three records a year. Most occur in May, with fewer in summer and autumn (a pair bred in Essex in 1950). Numbers occurring here have declined in recent decades, in line with a significant decrease in breeding populations in Denmark and Germany. Many recent records have been in western areas, suggesting over-shooting from Iberia, where significant populations persist. Historically, this species has a very high rejection rate, but this belies the fact that, if seen well, it is not difficult to identify.
Habitat and behaviour Unlike Sandwich Tern, Gull-billed is not a bird of the open sea and birders should be especially wary of claiming the species on sea watches. It typically occurs on coastal marshes, lagoons and estuaries, and also hawks insects over dry land; it may even be seen patrolling ploughed fields. It also catches larger prey, such as frogs, and one Norfolk vagrant developed a liking for Little Tern Sternula albifrons chicks. Unlike Sandwich Tern, it rarely plunge-dives.
Structure and flight An awareness of the structural differences between the two species is an essential first step to identification. Sandwich is a large tern, similar in size to Kittiwake Rissa tridactyla, and it lacks the long tail-streamers of Common S. hirundo, Arctic S. paradisaea and Roseate Terns S. dougallii. Compared to Gull-billed, it is a noticeably slim, rakish-looking bird with long, narrow, rather angled wings. The head and neck protrude noticeably and the bill is long and slender with a yellow tip (adults only). Although similar in size, Gull-billed is distinctive. In flight, it shows quite broad-based wings that are also long and pointed but tend to be swept back at the carpals. The overall effect may recall a small gull, while the slow, easy, rather languid flight also suggests Common Tern (indeed, the whole effect in flight may recall juvenile or winter-plumaged Common, rather than Sandwich). Rather bull-necked in flight. On the ground, it looks long-legged for a tern, with a rather horizontal carriage, but the most important feature is the thick and stubby black bill. It also tends to look short-necked and round-headed with a rather rounded belly and deep-based primaries.
Calls The calls of adults are totally different: Sandwich has a well-known shrill, guttural, rasping kerrr-ick, whereas Gull-billed has a low, deep ger-erk or ger-vik (quite unmistakable). Juveniles’ calls are quite different from adults’. Sandwich has a high-pitched, squeaky and rather sibilant sreee sree sree sree… or pree-peep pree-peep, often persistent and rather irritating. Gull-billed has a similar high, but soft pe-eep or a quick pe-pe-eep.
Plumage Adult summer In flight, Sandwich is a very whitish looking tern, with contrasting blackish outer primaries (these darken with wear as summer progresses). Adults may show a strong pink or a weak salmon tinge to the underparts. In flight, Gull-billed looks very pale, uniform whitish-grey above, including the rump and tail (Sandwich has a white rump and tail). However, in bright light, the upperpart colours of the two species can look surprisingly similar. Unlike Sandwich Tern, the underwings show an obvious blackish trailing edge to the primaries, similar to that shown by Common Tern (Sandwich has a more diffuse and much less obvious greyish trailing edge). Other plumage differences are less significant: when the head is raised, the black extends down the nape on Gull-billed (on Sandwich, the black is confined to the cap and the nape is white). Both species undergo a complete post-breeding moult. The primaries start with the inners in late summer, finishing with the outers in early to midwinter (on reaching the winter quarters); in late winter, the inner primaries are moulted a second time, prior to spring migration. The result of this moult is that, while in Europe, both species have old outer and new inner primaries. When new, the primaries have a pale grey bloom (radii) which is steadily lost with wear, revealing progressively more of the blackish base colour (rami). This produces a contrast between the old dark outer primaries and new grey inners, so that both species often possess noticeable dark outer primary ‘wedges’. In Europe, the wings look most uniform in spring, but dark outer wedges will be most pronounced in late summer and autumn, when the outer primaries are oldest. It seems, however, that, on average, Gull-billed wears less dark than Sandwich and usually shows less obvious primary wedges. Even as late as early September, some adults still look uniformly pale whitish-grey across the entire upperwing; at a distance, such birds look rather concolorous, showing little contrast between the upperwing and the underwing (according to BWP, about one-third of European Gull-billed do not replace their inner primaries a second time in late winter and such birds may account for at least some of these plain-winged individuals). Adult winter Adult Sandwich starts to lose the black on the lores, forehead and crown from mid June onwards so that, by late August/September, it has a prominent white forehead and black ‘shawl’ from the eye back over the nape. Individuals in full winter plumage by late July are probably non-breeders ( BWP). Adult Gull-billed starts its moult later than Sandwich, from late July to mid August, although some still have a full black crown in early September. A significant difference between moulting adults is that Gull-billed does not gradually acquire a white forehead; instead, the whole cap is moulted at once so that transitional individuals have the entire cap peppered with white. When moult is completed, Gull-billed has a completely different head pattern from Sandwich: instead of a black shawl around the nape, it has a white head with a variable grey or blackish patch immediately in front of and behind the eye, strongly reminiscent of first-year Mediterranean Gull Larus melanocephalus; this is faint on some, so these birds may look very white-headed from a distance. Some have very fine black streaking on the crown and nape (difficult to see in the field) while others have a grey wash to the rear crown (it seems that Gull-billed never has a black shawl). Juvenile Sandwich Tern Easily separated. Juvenile Sandwich has an all-black crown (including the forehead). However, it starts body moult soon after fledging so by autumn it acquires a white forecrown, a streaked rear crown and a black shawl around the nape (like winter adults). Initially, the upperparts are strongly patterned with dark brown and white (note in particular that this pattern occurs along the leading wing-coverts, unlike Gull-billed Tern; see below). However, during the late summer post-juvenile moult, much of the upperpart patterning is lost so that, by autumn, the mantle and scapulars are plain grey with variable traces of immaturity confined to the wing- coverts, tertials and tail (latter is mainly black). Note that the bill of juvenile Sandwich is often markedly shorter than the adult’s and lacks a yellow tip, thus looking stubbier; to the inexperienced, this could suggest Gull-billed so attention to plumage detail is essential. Whereas late summer adults have prominent black wedges in their outer primaries, juveniles have fresh pale grey primaries, the feathers narrowly fringed with white. Also note that juvenile terns can fly before their outer primaries are fully grown, so that recently fledged individuals have noticeably shorter, more rounded wings than adults; on Sandwich this, combined with the shorter bill, can suggest something unusual. Juvenile Gull-billed Tern Totally different from juvenile Sandwich. It lacks a black crown or shawl but instead has a small black ear-covert patch, like winter adult (very close inspection may reveal brown shaft-streaks on the crown and nape). Instead of being strongly patterned on the upperparts, the mantle and scapulars are relatively plain, usually appearing uniformly ginger in the field; by September, this colour fades to cream and is soon replaced by grey first-winter feathering. Note in particular the fairly plain wing-coverts, lacking Sandwich Tern’s dark feathering along the leading coverts. The overall effect is that, from a distance, juvenile Gull-billed looks very plain above and in flight can be difficult to separate from winter adult. Other differences include: the tertials are ginger with a brown feather centre and tip (juvenile Sandwich has the tertials strongly patterned with dark brown) and the tail feathers are grey with a pale tip and dark subterminal patch (on Sandwich, black, thickly edged with white). Note that, like adult, juvenile Gull-billed has a prominent dark trailing edge to the under-primaries. It may also show orange on the base of the lower mandible. First-year In early winter, towards the end of the post-juvenile moult, both species resemble winter adult, but are easily aged by retained juvenile tertial and tail feathers. First-winter Sandwich also has a dark secondary bar (absent on winter adult). By late winter, even these feathers are lost and both resemble winter adult. First-summer birds do not normally return to their breeding areas. Second-year Subsequently, both resemble adult but second-summer Sandwich does not attain full summer plumage, retaining white flecking on the forehead, lores and crown. Second-summer Gull-billed may show narrow white fringes to the black feathers of the cap and some vagrants, perhaps second-summers, have shown uneven wing-coverts with a slight brownish wash.
Roseate Tern S. dougallii
Note the similarity between juvenile plumages of Roseate (p. 245) and Sandwich Terns. Roseate is easily separated by size and shape, which are more similar to Common and Arctic Terns.
Forster’s Tern S. forsteri
Winter and juvenile Gull-billed may be confused with winter or juvenile Forster’s Tern, which also has a black ear-covert patch (20 British records 1980–2003, mainly in winter). Forster’s is easily separated from Gull-billed by the following features. 1 BILL Long and thin. 2 SIZE Much smaller (slightly larger than Common Tern). 3 STRUCTURE More similar to Common (in particular, it has a longer tail). 4 LEG COLOUR Pale (dull orange on firstwinter, bright scarlet on adult). 5 PRIMARIES Forster’s Tern usually has whiter primaries than Gull-billed.
Beware also of first-summer and winter-plumaged Common Terns (latter can occur from July onwards). These lack long tail-streamers, have an all-dark bill and a grey tint to the rump and tail. However, they are easily separated by size and shape, dark carpal bar and (when adult) red legs. First-summer Common Terns are similar to winter adults, but often show great contrast between the old, dark outer primaries/inner secondaries and new, grey inner primaries and outer secondaries.
Lesser Crested Tern Thalasseus bengalensis has occurred in Britain and Ireland, as have what are thought to be Elegant Terns T. elegans from W. North America. Any ‘Sandwich Tern’ with an orange bill should be carefully studied, photographed and expert advice sought. This is a very difficult subject, not least because hybrids may also complicate the issue.
Where and when Black Tern is a spring and autumn passage migrant, commonest in s. England, occurring at lakes, reservoirs, gravel pits and on the coast; large flocks sometimes appear, particularly during gloomy, anticyclonic weather. White-winged Black Tern is a very rare but annual spring (May–June) and autumn (mainly August–September) migrant, currently averaging 18 records a year, with a peak of 49 in 1992. Whiskered Tern is a vagrant, with records currently about eight a year, usually in April–June but rarely in autumn. Occasionally seen in small flocks, the largest being 11 in Derbyshire in April 2009. Its occurrences are normally independent of the other two species.
General features Small, compact terns and, compared to the larger Common Sterna hirundo and Arctic Terns S. paradisaea, they are rather stiff-winged, short-tailed and lack a prominent tail fork. They usually feed over fresh water and do not plunge for food (although Whiskered may belly-plunge on occasion). However, over fresh water Common and Arctic Terns also usually feed by surface-picking, just like marsh terns.
Structure White-winged Black is slightly shorter-billed than Black (recalling Little Gull Hydrocoloeus minutus) and has slightly shorter and rounder wings with perceptibly stiffer wingbeats.
Plumage Adult summer Easily separated. Black Tern has a black head and body, grey upper- and underwings and a grey rump and tail. In comparison, White-winged Black is a stunning bird: the head and body are black, but the forewing is white and the underwing-coverts are black (contrasting strongly with the pale grey under-primaries and secondaries). The rump and tail are strikingly white. On the upperwing, the outer primaries and inner secondaries are blackish, contrasting with the rest of wing. Its legs are red (blackish on Black Tern). Winter adult Autumn adult White-winged Blacks nearly always retain remnants of summer plumage, particularly traces of black on the underwing- coverts, white on the upperwing-coverts and the white rump and tail, making them readily identifiable. Individuals in full winter plumage are very rare in this country, but may be distinguished from Black Tern by the following features. 1 BREAST PATCHES Lacks Black Tern’s dark breast patches (often referred to as ‘breast pegs’) and the absence of this feature should be very carefully checked. 2 UPPERWING Paler than Black and, in autumn and early winter, has contrasting blackish outer primaries and inner secondaries, a result of feather darkening caused by wear; it also has a less obvious dark carpal bar on the leading edge of the wing-coverts. 3 RUMP Noticeably whitish compared to the grey rump of Black Tern. 4 HEAD The dark on the head is less extensive than on Black, producing a rather white-headed appearance in comparison: the black is confined to a small patch behind the eye and streaking over the rear crown (on Black Tern, the black is more solid and more extensive). Juvenile Black Tern has entirely plain grey upperparts with a browner mantle and scapulars, and a broad, dark carpal bar; from below, the ‘breast pegs’ are obvious. It is essential to check all of the following features before claiming a juvenile White-winged Black. 1 ‘SADDLE’ The dark brown ‘saddle’ (mantle and scapulars) contrasts sharply with the pale grey wings. Note, however, that in late autumn the dark ‘saddle’ may be less obvious owing to a combination of fading and the acquisition of the first grey winter back feathering; conversely, juvenile Black can look quite contrasting in certain lights. 2 WINGS Distinctly paler than juvenile Black Tern. 3 RUMP The ‘saddle’ also contrasts strongly with the white rump, which is obvious even at a distance, particularly when flying away. 4 CARPAL BAR Narrower and less conspicuous. 5 ‘BREAST PEGS’ Completely lacking. 6 HEAD PATTERN Like winter adult, the black on the head is less extensive, being confined to the ear-coverts and rear crown. First-summer Both species remain in their winter quarters during their first summer, but occasional individuals may move north with adults. Any Black or White-winged Black largely in winter plumage during the summer months is likely to be a first-summer, which often show strongly variegated plumage owing to the contrast between new and old feathering.
Hybrids Although hybrid Black × White-winged Blacks are rare, any White-winged Black should be checked for evidence of hybridisation. A juvenile hybrid in Somerset had the white rump, pale wings and dark ‘saddle’ of a White-winged Black, but the ‘breast pegs’ and structure of Black (Vinicombe 1980).
Structure Although obviously a marsh tern, Whiskered is larger and stockier than the other two which, along with its generally pale plumage, means that winter adults, juveniles and first-summers are far more likely to be confused with Common and Arctic Terns (see Common, Arctic and Roseate Terns). Structure is important: it has the typical Chlidonias shape, being rather stocky, neck-less and short-tailed (with only a shallow fork) with shorter, broad-based, straighter wings than Common. The bill is rather stubby, but it varies sexually, males having longer bills than females (no overlap). When perched, the legs are rather long and spindly.
Plumage Adult summer Easily identified. Very uniformly pale grey across the wings, rump and tail; it has a black cap and an obvious white face that contrasts with the blackish or dark grey underparts, which in turn also contrast with the white undertail-coverts. The bill is blood-red. Beware of confusion with darker-bellied Common and Arctic, or even with oiled individuals. Adult autumn Variable. Post-breeding moult commences as early as late June so autumn migrants usually show a patchy mixture of summer and winter plumage. Many soon acquire a white forehead or crown and gradually lose the dark grey underparts. Others may retain a complete black crown while losing the dark underparts. Adult winter White instead of dark underparts and the black on the head is reduced to a line through the eye and across the nape. The bill is black. Juvenile/first-winter Birds of this age are surprisingly rare in Britain. Juvenile has a dark brown ‘saddle’ (mantle and scapulars) with the individual feathers fringed buff (wearing paler). A rather restricted dark ‘breast peg’ extends onto the neck sides. However, unlike the other two species, Whiskered starts to moult soon after fledging, so full juvenile plumage is rare here. By the time they migrate, most have lost or started to lose much of their dark juvenile mantle and scapular feathering, so late autumn juveniles/first-winters look rather plain grey above but often have some dark brown on the scapulars. Juveniles have a dark bill and legs, and small areas of black confined largely to the ear-coverts and rear crown. First-summer First-summer Whiskered seem to return north more regularly than other terns. Although some are apparently adult-like, others have the underparts mainly white, with only a few dark feathers (individually variable).
Eliminating Common and Arctic Terns Whiskered in non-breeding plumage is easily identified by its typical Chlidonias shape and pale grey upperparts. Common and Arctic Terns of all ages have a longer, more deeply forked tail and long wings that, in the case of Common, produce a more languid flight action. For plumage and other details, see Common, Arctic and Roseate Terns–Roseate Tern Sterna dougallii.
First recorded in Britain in 1999, this potential split has now occurred here five times (1999–2012) as well as four times in Ireland (to 2007). It is likely to have been overlooked previously. All British records have related to late autumn juveniles which can be distinguished from juvenile Black Tern by (1) extensive grey on the breast-sides and flanks; (2) greyish underwing-coverts (as opposed to white); (3) darker and more uniform upperparts (including the rump) and (4) a paler grey crown (with white flecks) contrasting with black ear-coverts (Andrews et al. 2006). Any juvenile Black Tern showing a combination of such characters should be photographed and expert advice sought.
References Andrews et al. (2006), Vinicombe (1980).
Where and when Common Tern is a widespread coastal and inland-breeding species, with a protracted spring and autumn migration; in summer, non-breeders may occur far from traditional nesting areas. Arctic Terns predominate in n. Britain, passing through southern areas mainly in late April and early May and again from late July to October (with a peak in September). It is more pelagic than Common, with the bulk of the passage apparently in the Atlantic; it would appear that relatively few use the English Channel as a migration route. It is, however, frequent inland on passage, although the largest numbers tend to follow westerly gales. Otherwise, only in late September and October (when most are juveniles) do Arctics usually outnumber Commons in southern areas. Roseate Tern currently breeds mainly on Coquet Island, Northumberland (80 pairs in 2010) with a few pairs scattered elsewhere. A much larger population occurs in Ireland, on Rockabill Island, Co. Dublin (1,080 pairs in 2011). Significant post-breeding gatherings may occur near the breeding colonies, otherwise, very small numbers are recorded around the coast on migration, mainly in eastern and southern counties; it is exceedingly rare inland.
Approach to identification Because of identification difficulties, many observers lump Common and Arctic as ‘Commic’ Terns but, with the exception of distant birds, the two species are readily separable, although thorough practice is essential. It must be stressed that in most of England and Wales, Common Tern is far more numerous than Arctic, both as a breeding bird and on passage, and it should not be assumed that both species occur in equal numbers.
Structure At rest, Common is slightly but distinctly larger and sturdier than Arctic, with a longer bill, neck and legs; in flight, adults are distinctly longer-winged and proportionately shorter-tailed. At rest, Arctic is more delicate and in many ways its structure is reminiscent of a marsh tern Chlidonias. Note that resting birds appear neckless, a rounded head merging seamlessly with the body; they also have a shorter bill and noticeably short legs. In flight, Arctic has shorter, more slender wings, a consequence of a shorter ‘arm’ and narrower, more pointed primaries; it also has a strikingly long tail. It is useful to remember that Arctic’s overall shape is reminiscent of a Swallow Hirundo rustica, with a similar ‘short-headed/narrow-winged/long-tailed’ shape. From below, its wings often form an inverted W shape, with the ‘arm’ pushed forward and the sharply pointed primaries angled back, more so than Common. Although lacking long tail-streamers, juvenile Arctic is nevertheless distinctly long-tailed compared to the more evenly proportioned juvenile Common. Note that recently fledged juveniles of both species fly before their outer primaries are fully grown, so young juveniles close to their breeding sites may have shorter, more rounded wings than adults (but their wings are fully grown by the time they migrate).
Flight Common Tern’s long wings produce an easy, languid flight action, and the wings usually look quite bowed when head-on. Arctic has slightly but distinctly shallower, quicker, wingbeats. When surface-feeding inland, Commons have a steady flapping flight, continually dipping to the water’s surface, whereas Arctics tend to fly higher (maybe 3–5m), stall, and then stoop steeply to the surface; however, both also patrol lower over the water, rapidly picking off insects with a downward head movement. Note that migrating birds of both species frequently fly low and fast over the sea, often in large groups, with angled-back wings and ‘whippy’ wingbeats; such birds are often impossible to identify, especially at a distance (see ‘Distant birds’ p. 246).
Plumage Adult summer Pay particular attention to the following features. 1 UPPER PRIMARIES Common moults its inner primaries twice a year (in late summer and late winter) but the outers are moulted only once (in early winter). Consequently, in Europe there is usually a contrast between the new inner primaries and the old outers. When new, the feathers have a pale grey bloom (radii) that is steadily lost with wear, revealing progressively more of a blackish base colour (rami). Consequently, the older outer primaries are darker than the newer inners, producing a large dark wedge that is obvious at some distance. However, it is important to remember that the contrast is most obvious in late summer and autumn, and least obvious in spring, particularly at a distance. It must be stressed that, in spring and summer many lack a dark wedge while many others show only a small one confined to the middle primaries and this can be difficult to detect at any distance; as a consequence, such birds are routinely misidentified as Arctics (see ‘Distant birds’ below). Arctic Tern has a complete wing moult once a year (in late winter, prior to spring migration) so the primaries are always similarly aged. Consequently, they always appear uniformly pale grey throughout the species’ stay in the Northern Hemisphere, never showing Common Tern’s dark primary wedges. 2 UNDERWINGS Common has rather silvery-grey underwings with a broad, diffuse dark grey trailing edge to the under-primaries (visible at some distance); also, when viewed against the light from below, only the inner primaries appear translucent. Arctic has very white underwings (recalling Kittiwake Rissa tridactyla) with a narrow, neat, clear-cut black trailing edge to the under-primaries. When viewed against the light, the whole of the under-primaries appear translucent. 3 BILL Bright orange-red with a black tip on summer Common, the red being obvious at a considerable distance. In contrast, Arctic has a shorter, stubbier and darker blood-red bill. It must be stressed, however, that both have black bills in winter, and some spring and autumn Commons, as well as second-summers, show a black bill (or dark red with a black tip) as well as a white forehead. Similarly, some spring Arctics have dark red merging into an inconspicuous black tip. Nevertheless, any ‘Commic’ Tern with a long, bright orange-red bill with clear-cut black tip is safely identifiable as a Common, but it is not safe to identify darker-billed individuals without reference to other characters. 4 UNDERPARTS Spring Arctic tends to have darker grey underparts, but some Commons are also quite dark (individual variation and vagaries in the light make this a difficult character to evaluate). 5 HEAD When perched, the black on the head of adult Common extends further down the nape, whereas the shorter-necked Arctic has a more rounded black ‘skull cap’. 6 DISTANT BIRDS It must be stressed that distant birds, particularly in spring, need to be identified with caution as the pro-Common features, such as the dark primary wedges, may be very difficult to see or may even be absent. The best way to separate such birds in spring is by a combination of shape, underwing colour and the pattern of the under-primary tips, but this requires practice. Distant spring migrants on sea watches are particularly problematic and are usually best logged as ‘Commic Terns’ (see also ‘Flight’). Juveniles Easily separated, even at a distance. In southern areas, the first migrant juvenile Arctics (mainly late August to October) really stand out from the more familiar juvenile Commons, which pass through from mid July onwards. As well as the structural differences outlined above, the following plumage features are significant. 1 WINGS On the upperwing, Common has a thick, blackish carpal bar, a grey secondary bar (narrowly tipped white) and grey primaries. In contrast, Arctic lacks an obvious carpal bar but, most importantly, it has essentially white upper-secondaries and paler, whiter primaries; therefore, the entire rear wing often looks strikingly white, even at a distance. This impression of whiteness is further emphasised by the ‘Kittiwake-white’ underwings, with a narrow, clear-cut black trailing edge to the primaries. When viewed against the light, the underwings of juvenile Arctic often appear strikingly translucent. 2 UPPERPARTS Common shows a distinct ginger-buff tone to the upperparts, with narrow dark scalloping, both of which soon fade. Young Arctics show fainter pale buff tones to the upperparts and delicate dark scalloping, but these too also fade, so that autumn Arctics have pale grey upperparts that appear much ‘cleaner’ than those of Common, forming a contrast with the much whiter primaries and, particularly, secondaries. Common also has a greyer rump. 3 BILL Common usually shows more orange at the base of the bill (bill all black on Arctic, although recently fledged juveniles can show some red). Adult winter Structural and underwing differences remain the same as in summer. Certainly by August, and sometimes even in July, adult-type Commons may show signs of winter plumage; indeed, some attain full winter plumage by time they head south. As well as acquiring a dark bill and a white forehead, winter adults have a dark carpal bar, traces of a dark secondary bar, a grey tail and grey-washed rump. Moulting individuals often look rather worn and tatty. Winter-plumaged Commons may confuse beginners and suggest marsh terns, particularly on inland fresh water where, like marsh terns, they feed mostly by surface-picking, rather than plunge-diving (several erroneous claims of Whiskered Terns C. hybrida have proved to be winter adult, or even juvenile Commons). Before leaving our shores, adult Arctics may acquire a black bill and white forehead but otherwise show very little sign of moult until their arrival in the winter quarters; consequently, any ‘Commic’ Tern showing signs of wing moult in autumn should be a Common. Immatures Unlike gulls, immature Common Terns do not show clear-cut age related plumages during the breeding season, so their accurate ageing is not usually possible (White and Kehoe 2001, upon which much of the following is based). The vast majority of first-summer Common and Arctic Terns remain in their winter quarters but a few head north. First-summer Common is similar to winter adult and individuals undergoing active wing moult may have worn one-year old dark outer primaries that contrast with fresh grey inners; it is only these moulting birds that can be accurately aged. This is because many first-summers have already completed their moult and replaced all their juvenile primaries, rendering them indistinguishable from second-summers. The great majority of second-summer Commons return to the breeding grounds but most are indistinguishable from the adults (although some show white on the forehead and an all-dark bill). However, most adult-like second-summer Commons show little contrast in their primaries, with some showing evenly pale grey upper primaries with only a faintly darker grey inner primary wedge. Such birds may suggest Arctic Tern, particularly at a distance. Some immature Arctic Terns also return north in summer and most seem to have uniformly fresh, adult-like pale grey primaries and also new tail feathers (but they lack the very long streamers of adults). Otherwise, they are similar to winter adult, with a black bill, a large white forehead and a faint dark carpal bar (smaller and less obvious than on Common); maybe also with the odd grey feather in the underparts. Whether such birds are first-summer or second-summer is not clear but they lack the strongly patterned plumage of first-summer Common, appearing more uniform and more adult-like.
Calls Common’s various calls include a muffled kik, a familiar rolling keea-ya and a characteristic, grumpy keeyar. Common’s calls are fuller and throatier than those of Arctic, whose equivalent calls tend to be slightly thinner and less rasping. Juvenile Commons have a repetitive guttural begging call sri-sri-sri-sri-sri…, often rapidly alternated with the adult’s answering kik. Begging juvenile Arctic gives a thin, high-pitched, musical pi-pi-pi-pip.
Structure Slightly smaller and more delicate than Common, with shorter, narrower wings that appear more centrally placed on the body. Extremely long tail-streamers (even longer than Arctic’s) which may quiver up and down in flight. The head and neck project slightly further than the other two species.
Flight Stiffer flight action than Common. When feeding, it may fly around in tight circles with quick, fluttery wingbeats, followed by a steep dive towards the water.
Plumage Adult summer Remember that Roseate shares many plumage characters with the larger Sandwich Tern Thalasseus sandvicensis. Like that species, the upperparts are very white, but a key feature is that, unlike Common and Arctic, Roseate lacks a dark border to the under-primaries, showing at best only a slight darkening (difficult to see in the field). Like Sandwich, the underparts show a delicate rose-pink flush in summer. Like Common, it acquires dark blackish primary wedges as summer advances, these contrasting conspicuously with the very pale upperwings. Any very white ‘Commic’-like tern that shows blackish primary wedges should prove to be a Roseate (but beware of confusion with the much larger Sandwich Tern). The bill is slender and black (usually with variable amounts of red at the base) but remember that both Common and Arctic can show black bills, even in midsummer. Other differences include: (1) the cap tends to go straight back from the bill at rest (rather than curving up behind the eye like Common) and (2) the feet and longer legs are extremely bright orange (recalling Puffin Fratercula arctica). They may acquire a white forehead before migrating in autumn. Juvenile Easily separated from Common and Arctic, and bears an uncanny resemblance to a miniature juvenile Sandwich Tern. It has a completely dark head with an all-dark forehead (but the crown is sometimes slightly paler and some start to acquire a white forehead by late September). The mantle and scapulars are strongly scalloped with dark brown, forming a distinctive ‘saddle’ in flight. The wings are similar to those of juvenile Common, with a variable dark carpal bar, but it lacks the obvious dark tips to the under- primaries. Also, unlike Common and Arctic, the legs are black. First-summer Usually remains in the winter quarters, so very rare in Britain. It resembles adult (also shows dark outer primaries) but has a white forehead, an obvious dark carpal bar, a black bill and blackish legs.
Calls Adult has a diagnostic, high-pitched, shrill, slightly rasping tch-wit or tchu-weet, in quality somewhere between Sandwich Tern and Spotted Redshank Tringa erythropus. Also, an equally characteristic harsh, rasping zraak. Begging calls of juvenile are a thin, squeaky zi-zi-zi-zi-zi-zi…; later calls are similar to the adult’s but shriller and squeakier.
References Scott & Grant (1969), Grant & Scott (1969), Grant et al. (1971), Hume & Grant (1974), Hume (1993), White & Kehoe (2001).
