Where and when Both Slavonian and Black-necked Grebes are very rare breeding species (the former rapidly declining in Scotland, the latter at scattered sites in England) but are more widespread as coastal winter visitors and passage migrants. In Britain, Slavonian is locally common from September to April, with Icelandic immigrants increasing in n. Scotland but Continental birds declining around e. and s. England (Harvey & Heubeck 2012); it is scarce and local in Ireland. Slavonian frequents sheltered bays, estuary mouths and harbours, and sometimes occurs inland, mainly in late autumn and winter, often during spells of severe freezing weather. In winter, Black-necked Grebe is distinctly rarer than Slavonian, with a more southerly distribution, occurring locally off s. England (mainly Dorset and Hampshire). It is rare in Ireland. It prefers more sheltered environments than Slavonian and is less likely to be seen riding out rough seas. It also turns up inland, particularly on reservoirs, but mainly from July to November and again in early spring; it is rare inland in midwinter. Red-necked Grebe is the rarest and is mainly an uncommon and apparently declining winter visitor from September to April (current winter population estimated at 55). It is most frequent off coasts of e. and s. Britain; it, too, is rare in Ireland. There is an annual late summer moult gathering in Gosford Bay in the Firth of Forth (recently around 50, but now reduced). It may be much more widespread in severe winters, even inland (c. 500 were recorded in 1978/79).
Size and Shape Both are small black-and-white grebes closer in size to Little Grebe Tachybaptus ruficollis than to Great Crested P. cristatus. The simplest way of separating them is by overall shape and by their head patterns. A useful aide-mémoire is to think of Slavonian as a miniature black-and-white Great Crested and Black-necked as a large black-and-white Little Grebe. In shape, Slavonian suggests Great Crested Grebe in that it has a rather low forehead, a flat crown and a peak at the rear of its head. The back, too, is rather flat with the rear end tapering off towards the water’s surface; it may, however, appear more fluffed up and rounded when resting. Compared to Slavonian, Black-necked is altogether a more rounded, fluffier-looking bird, with a high, steeply sloping forehead with a distinct peak either at the front or in the centre of the crown. It has a rather thin neck, the back is rather more rounded than Slavonian and the rear end tends to be held higher and more fluffed out, the whole shape being strongly reminiscent of Little Grebe, with which it often associates.
Bill Slavonian has a straight, pale-tipped bill, whereas Black-necked has an uptilt to the lower mandible, but this can be surprisingly difficult to detect at any distance, particularly on juveniles.
Plumage Slavonian Even at a distance, Slavonian is a small, smart, black-and-white grebe, again suggesting a miniature Great Crested. The black cap extends straight back from the bill and through (but not below) the eye. It is thus sharply demarcated from the gleaming white face and cheeks. At close range, it often shows small pale patches on the lores (usually lacking or very tiny on Black-necked). The breast is white but variable amounts of dark shading may extend around the upper foreneck (perhaps strongest on first-winters). Adults moult in late summer/early autumn so they may retain traces of summer plumage into October. Early autumn juveniles are similar to winter adults, but rather less clean-cut and they may retain traces of head striping behind the eye and on the lower cheeks. Post- juvenile moult continues throughout early winter, so that first-winters and adults are soon indistinguishable (the adult’s brighter red eye may be the best difference). Black-necked Unlike Slavonian, in winter Black-necked the black of the head extends below the eye with a prominent lobe of white extending up behind the eye into the black of the rear crown (the black cap bears an uncanny resemblance to a showjumper’s hat). The whitish ear-coverts and throat are generally dingier than Slavonian but the face nevertheless contrasts with the dull greyish foreneck, which in turn contrasts with the white breast. Thus, the overall effect is of a drabber, messier bird than Slavonian. This dingier appearance is especially true of autumn juveniles which, as well as being slightly browner than winter adults, show a dull orangey tint to the ear-coverts (often misinterpreted as remnants of summer plumage) as well as a dark line behind the eye. Also, juveniles have dull orange eyes (brilliant red on adult). By late autumn, all ages look much more black and white and some smarter individuals can suggest Slavonian, especially at a distance. Eye colour is probably the best ageing feature by then. Note that, in March/April, winter plumage differences often ‘break down’ as both species start to moult into summer plumage. Of interest, Black-necked Grebes may call in both spring and autumn: a high pitched upslurred oo-ee or pee-eep.
Flight identification Slavonian’s wing pattern is similar to Great Crested’s with variable amounts of white on the inner forewing and a large white patch confined to the secondaries. Black-necked lacks white on the forewing but the white patch on the rear of the wing is larger, extending onto the inner four or five primaries (although differences may be difficult to evaluate on the rapidly moving wing).
Other confusion species Beginners may confuse Slavonian and Black-necked Grebes with other species. Particularly pale or contrasting winter-plumaged Little Grebes may be mistaken for juvenile Black-necked, but note Little’s essentially brown upperparts and buff underparts. Great Crested Grebe may be confused with Slavonian, but the former is larger, longer-necked, browner above, has a prominent white line above the lores and, most obvious of all, a long pink bill. Also, although Great Crested has red eyes, they do not stand out and ‘glare’ as much as Slavonian’s. Distant winter Slavonian may be confusable with auks, but the latter have short, thick necks, longer bodies, a longer tail (only Razorbill Alca torda) and distinctive open-wing diving actions.
Size and shape Intermediate in size between Slavonian and Great Crested, but distinctly shorter-necked, stockier and more compact than the latter.
Bill Rather dagger-like, on juveniles and first-winters pale yellow (sometimes greenish); on adults black with a prominent bright yellow patch at the base, sometimes extending towards the tip, particularly on the lower mandible (bill pale pink on Great Crested).
Winter plumage Remember that the pattern of juvenile and winter plumages reflects that of summer adult: pale face, dark neck and pale breast. Consequently, compared to Great Crested (which is gleaming white below) Red-necked looks dull and scruffy. Whereas Great Crested has an obvious white line above the lores, Red-necked has a black cap that extends down to the eye. Dingy whitish cheeks then contrast with a darker neck, which varies from buffy-brown through brownish-grey to quite a dark purplish-brown. Blacker above than Great Crested and usually shows a striking white flash along the upper flanks. Distant birds are perhaps more likely to be confused with Slavonian Grebe, particularly those with dark shading on the neck, or transitional ones in spring that have started to acquire orange summer neck feathering. If in doubt, check the bill colour.
Juvenile In early autumn, juveniles are surprisingly similar to summer adults, with a strikingly chestnut neck that contrasts with the whitish face; however, young birds often show prominent black head striping. This plumage is lost after a late autumn/early winter post- juvenile body moult, although vestigial head striping can persist well into the winter.
Flight On autumn and winter seawatches, Red-necked appears similar in size and wing pattern to Great Crested, but is somewhat stockier and shorter-necked. Its dusky head and neck are in marked contrast to winter Great Crested, which always looks very white in these areas.
Diving actions When feeding in deep water, Red-necked often leaps well clear of the surface, rather like a Shag Phalacrocorax aristotelis. Unlike Great Crested, fish are often brought to the surface and manipulated before swallowing. Great Crested usually submerges smoothly, without leaping. Slavonian and Black-necked tend to spring forward with a quick, dapper action. However, such differences are not diagnostic and, in general, the deeper the water the more energetic the diving action.
Reference Harvey & Heubeck (2012).
