CHAPTER 4
Ptarmigan
THE PTARMIGAN IS THE world’s most polar bird, living over vast areas at or near sea-level in the Arctic. Rocks and ptarmigan usually go together, and North Americans call the bird rock ptarmigan, a usage that has spread. A Scottish writer in the early 1700s noted, ‘that fine bird called the Mountain Partridge, or by the commonalty Tarmachan…makes its protection in the chinks and hollow places of thick stones from the insults of the eagles’.1 Here we describe its habits and report its distribution, habitat and adaptations to cold. We summarise many studies on the populations, nests and breeding success of this grouse species.
Ptarmigan nest on northernmost Canada, Greenland, Svalbard and Russia. In winter they remain in all but the most northerly parts, and live year-round in Svalbard despite midwinter darkness at noon. Birds wintering in the Arctic live in regions with mean January air temperatures down to -35°C. Willow ptarmigan in subarctic Siberia winter at even lower mean January air temperatures of-45°C, but this is in sheltered valleys with far less wind-chill than on the windswept reaches frequented by rock ptarmigan. The latter also thrive on southern mountains such as the Alps. Our high Scottish hills are home to large numbers of the species, the only birds resident at all seasons in this wildest part of Britain.
The high Scottish hills also attract many human visitors, but even expert mountaineers must take care here when navigating in a whiteout or scaling steep snow or ice, and in a snowstorm must take shelter or risk hypothermia and death. To study Scottish ptarmigan in winter and spring, one must be a mountaineer and skier, but nobody can remotely match the ptarmigan’s intimate knowledge of its home terrain, or its hardiness and superb ability to thrive in this extreme environment.
Also to be admired is the ptarmigan’s plumage.2 Soft feathers reach to its toenails and cover its nostrils, so it loses little heat on cold days. The plumage alters from spring to summer and from summer to autumn, the richly variegated grey, brown, white and black blending with rocks and plants to conceal the bird. Its white winter dress contrasts with its dark eyes and black bill and tail-quills, the last appearing only in flight. When a snow-white cock and hen pair on a sunny spring morning, one hears them answering each other from far away. His rattling croaks and her weird coos echo across the snowy slopes. Amid gleaming silvery light on the snow and patches of brilliant green plants freed from winter’s grip, these birds are the first spring voice of the heights of Scotland.
THE BIRD
Dimensions
The Scottish ptarmigan is the smallest of British grouse, slightly shorter than a wood-pigeon, with cocks about 5 per cent longer than hens.3 Scottish cocks have an average wing length of 198mm, while Svalbard cocks – the largest race – have an average of 230mm.
Scottish cocks weigh 500-550g, and are heaviest in March and lightest in April-June. Cocks exceed hens in weight in every month except in spring. At this time, hens fatten and increase their breast muscles in preparation for breeding, while cocks are busy with territorial activity and lose weight. Hens in May attain 625g, easily surpassing the cocks’ 500g. By June, however, cocks still weigh 500g but hens are down to 470g, signifying the toll of incubating for three weeks with only brief trips to feed.
Rock ptarmigan are about 10 per cent smaller than Lagopus lagopus in the same region, and they have narrower wings, a slighter build and a more dove-like silhouette. Even so, the bigger races weigh more than small races of willow ptarmigan in other regions. For instance, rock ptarmigan of Alaska’s Amchitka Island outweigh the willow ptarmigan of central Alaska.4
The ptarmigan’s wings and tail are long relative to its body size, enabling it to fly fast when chased by raptors and making it the fastest of British grouse. The birds also make split-second turns into rocks, which is a useful habit as raptors avoid flying quickly beside rocks for fear of injury. Ptarmigan sail adeptly on turbulent currents. Seton Gordon considered them superior in flight power to red grouse, for ‘they can wing their way up a steep hill face at a surprising speed’,5 and are ‘remarkably strong fliers, possibly the strongest of all grouse’.6
When flushed, ptarmigan seldom fly far up or down a steep slope, but traverse round at similar altitude, often to return shortly after. However, they readily shoot up or down cliffs to escape a chasing eagle, a demanding tactic that may be aided by their large hearts.
Birds in interior Alaska are small, weighing only about 425g in winter,7 and the smallest Siberian birds also live in the interior of that region.8 Small birds typify regions with very cold winters and deep undrifted snow, where they keep warm by burrowing (see Fig. 12). On oceanic Amchitka Island, where frequent gales blow the ephemeral snow, birds in winter weigh about 575g.9 The heaviest ptarmigan live on windy Svalbard. These birds avoid the risk of migrating over the Arctic Ocean to Norway, and instead remain resident through the midwinter darkness10 and survive by laying down fat reserves in autumn (see ‘Metabolism’, p.86).
The rock ptarmigan has the largest heart of the grouse family as a percentage of its body weight; the willow ptarmigan’s is smaller and the white-tailed ptarmigan’s smaller still, even though the latter live at higher elevations.11 Perhaps the rock ptarmigan’s large heart evolved because the birds are such strong fliers. This would have helped them colonise distant islands such as Iceland or Japan, which have no Lagopus lagopus.
Plumage
The only British bird to grow a white winter dress, the ptarmigan has three plumages, each attained by a partial moult of the old and growth of the new. In all seasons, it has white wings. Viewed from the front, during the moult from winter to summer, cocks show a broken dark frontal necklace in display to hens or other cocks (see Fig. 5). Scottish cocks in full summer plumage have greyish backs, their dark heads, necks and breasts contrasting with a few white feathers remaining from the winter. A gorgeous pale golden yellow is the hen’s summer dress, her feathers heavily marked by bars of black and white, a varied pattern that provides superb camouflage when she sits on her nest or chicks. Both cock and hen in autumn are silvery grey and are more alike, the hen slightly paler and with more of a salt and pepper appearance (see Chapter 10).
Within the white winter dress, many Scottish birds show a few dark feathers on the back and head. Cocks also have a wide black bar running from the hind end of the black bill past the dark eye, whereas hens lack this or show rudimentary black spots.12
Eggs and chicks
Oval in shape, the ptarmigan’s eggs (see Fig. 13) resemble those of red grouse except that they are smaller, with a paler ground colour and markings that are
FIG 29. Scottish ptarmigan in winter plumage. (Top) The cock’s throat swells and vibrates as he calls threateningly (known as ‘ground beck’; see Chapter 7). (Bottom) The hen is giving the same call in her higher pitch. (Derek McGinn)
FIG 31. Scottish ptarmigan cock moulting from winter to summer plumage, with the frontal necklace beginning to develop. (Derek McGinn)
FIG 32. Scottish ptarmigan cocks in summer plumage, with combs raised (top) and giving ground beck (bottom). (Derek McGinn)
FIG 34. Scottish juvenile hen ptarmigan in autumn. (Derek McGinn)
less reddish. Though they are paler than their surroundings, the eggs have a contrasting dark and light pattern that camouflages them well, making them difficult for even experienced observers to spot. As in the other three British grouse, hatching takes about a day.
Day-old chicks can climb steep rocks and run over boulders better than Lagopus lagopus of the same age. When suddenly disturbed on steep ground, they escape by rolling like balls down vegetation and rocks without harm, and quickly pop down holes among boulders until the hen calls them out after danger has passed. Day-old chicks can easily swim if they fall into water, and older chicks swim strongly.13
Soft down covers day-old chicks to their toenails. They grow quickly,14 reaching full size slightly more rapidly than Lagopus lagopus. Scottish poults at ten weeks are hard to tell from adults in the field, although they have a more pointed tail and traces of down on the belly, and occasionally give thin cheeping calls when out of sight of their mother. By 12 weeks they look as big as adults, but can still be told in the field by the narrower bands of pale pigment on their flank feathers. The presence of a partly dark, wide-barred inner secondary or upper covert signifies a young bird, and sometimes it falls off as the bird takes wing. Poults attain adult weight by the end of October.15 In his book of paintings, Keith Brockie illustrates a fine series of ptarmigan, from a day old to fully grown.16
CAMOUFLAGE
Ptarmigan stay motionless so effectively that hikers often pass birds without seeing them sitting a few metres from their boots. In autumn they can be shot easily on some warm days, though they are wilder than red grouse in late-autumn gales or rain. They are at their wildest when in white or partly white dress on snow-free ground, when they are conspicuous even at 1km. In such conditions they spend much time resting beside rocks or at remnant snowdrifts, which they frequent ‘throughout the day, venturing off only a short distance to feed’.17
Ptarmigan are easily overlooked, however, when many small patches of snow lie on dark ground, irrespective of whether the birds are white or dark. Because of the strong contrast between the light and dark, the human eye cannot easily discern such detail as an individual bird, and doubtless this goes for predators too. Ptarmigan are confiding in such conditions, and are hard to see even when they move while feeding. When in dark plumage they avoid pale backgrounds, especially nesting hens. Hence they seek places where their colour at that time is cryptic,18 as do all Lagopus species.19
FIG 36. The same nest after hatching – the late chick died. (Stuart Rae)
SYSTEMATICS
The rock ptarmigan (Lagopus mutus) is closely related to Lagopus lagopus, the willow ptarmigan (including the red grouse). Over 20 subspecies or races have been described, mostly from isolated southern islands and mountains. Races have been grouped according to autumn plumage: grey in mainland Europe and Scotland, and brown from the Urals east across America to Greenland, Iceland and Svalbard.20 The summer plumage also shows some variation between races. Cocks in the European continent and Scotland have grey backs with some black on the breast, neck and head, but on Canada’s high-Arctic islands and Greenland they are more sandy.21 The darkest race in the world lives on Attu in the Aleutian Islands, where cocks have an almost black summer plumage. In contrast, on Bering Island towards Japan they are much paler, and in Japan itself they are darker than on Bering Island, resembling Scottish cocks.
Birds with a continuous range over vast areas show little variation even though they live thousands of kilometres apart. One race lives from the Urals east to Canada’s Mackenzie River and south to the eastern Aleutians. A second occupies north Greenland and the northernmost Canadian islands, and a third the rest of Canada’s Arctic islands and the mainland from the Mackenzie River south to central British Columbia and east to Labrador.
Ptarmigan that are geographically isolated in the Aleutians can differ in plumage colour between one island and another, and a recent study using DNA revealed greater genetic variation between the Aleutian races than within continental Alaska or Siberia.22 Three races in the central Aleutian Islands have a similar pale summer dress, tending towards buff, while dark races occur on islands to the east and west.
WORLD DISTRIBUTION
Ptarmigan breed down to sea-level in the Arctic and up to an altitude of 3,000m on some southern mountains. The species’ circumpolar distribution encompasses rocky tundra, with isolated offshoots south to 35°N in Japan, and to Bulgaria.23 A claim that they occur at a latitude of 39° in the Pamirs of Tadjikistan24 has, however, been challenged.25
Ptarmigan inhabit Greenland, Iceland, Norway, Sweden, Finland, much of northern Russia from Kola and the Urals east to the Bering Strait and south to Kamchatka, and the Commander and northern Kurile islands. They occupy mountains around Lake Baikal, and the massifs of Sayan, Altay and Tarbagatay that straddle south Siberia, Mongolia, Sinkiang and Kazakhstan.
Excluding tiny islets, they breed on the nearest land to the North Pole, on the tips of Ellesmere Island and Greenland. One was shot in 1876 on Ellesmere at 82°46’N, and footprints were seen in 1882 on an island at 83°24’N on Greenland’s northern tip.26 Ptarmigan inhabit Franz Josef Land,27 but they have not been recorded on Novaya Zemlya, Severnaya Zemlya or Novosibirskye Ostrova. The large race hyperboreus lives on Svalbard, Bear Island and Franz Josef Land.
In America, ptarmigan range from the Aleutians and mainland Alaska through northern British Columbia to Labrador, across the Canadian Arctic islands, and southwards along the Coast Mountains north of Vancouver and on hills in Newfoundland. Greenland birds spread quickly after being released on the Faeroes in 1890 and Scottish red grouse were introduced there about six years later. A few birds of unknown species, including a nesting hen, remained on a northern island in the 1960s.28 Apparently they have now gone, probably as a result of overgrazing by sheep.29
DISTRIBUTION IN BRITAIN
Authors in the late 1700s mentioned ptarmigan in the Lake District, and a specimen taken on Skiddaw appeared in a local museum, but by the 1820s none was seen by men who knew the hills well.30 Ptarmigan were shot on the Southern Uplands in the late 1600s, reported in the 1700s, and shot in winter around 1822-3,31 and in 1826 one was seen on the Merrick hill.32 An introduction to the Southern Uplands in the mid-1970s apparently failed, as did one in Donegal, Ireland, in the late 1800s.33
Ptarmigan bred on Hoy in Orkney up to 1831.34 They lived on the Outer Hebrides into the 1900s,35 and were still on Harris in the early 1960s.36 In the 1800s they occurred on Skye, Rum, Mull, Jura and Arran, and a pair produced young on Scarba in 1959.37 They bred on Arran in 1977 and subsequently, and in the 1980s were on Skye, Rum, Mull and Jura.38 In the 1990s and first years of the twenty-first century they have been seen on Arran in most years, including breeding birds, and on Mull in several years.39
On the Scottish mainland they breed from Ben Lomond northwards to Sutherland and Caithness, and east to Mt Keen.40 On the isolated Ben Rinnes of Moray and Mt Battock near Aberdeen they have reared broods in some recent years, though in others no birds were seen.41 In the late 1800s, they inhabited hills at Cabrach and Glen Livet,42 but since 1950 only an occasional unmated cock has been seen there in summer.
In winter there are occasional records on low eastern hills where no bird has been seen in summer.43 One was on a 378m hill in late April 1947, and in November 1953 a cock was seen on a few acres of heather along a coastal cliff top south of Aberdeen.44
The ptarmigan’s range in Britain has contracted over the centuries as overgrazing by sheep has left little heath as food and cover on the high hills of England, Wales, Ireland, the Southern Uplands, the Inner and Outer Hebrides, Orkney and many hills of the Highlands. Increases in numbers of red deer have exacerbated this on most Alpine land in Scotland and England, and in much of Ireland too. Hills south of the Highlands could hold ptarmigan again if overgrazing were ended and heath restored.
NATIONAL AND REGIONAL NUMBERS
Because so few counts of ptarmigan have been carried out, different estimates vary greatly.45 One estimate for North America that allowed for fluctuations was 2.1-8.4 million adults in June, and 3.7-24.3 million birds in September.46 A recent publication lists the largest population estimates as over a million breeding birds each in Canada and Alaska, 700,000 in Russia, 100,000-500,000 in Iceland, 150,000 in Sweden and over 100,000 in Greenland.47
An often repeated estimate for ptarmigan numbers in Scotland is at least 10,000 pairs in spring.48 More accurate estimates for the Cairngorms massif alone, based on counts, ranged from 1,300 birds in a spring of low numbers to 5,000 in a peak spring and 15,000 in a peak autumn.49 Since then, a 1.6-fold higher peak came in 1971 on the Derry Cairngorm study area, so earlier estimates have been exceeded.
HABITAT
Habitat and physical cover
Alpine vegetation is usually too short to conceal a bird as big as a ptarmigan, even when it crouches. Instead, it uses rocks as cover. Adults are adept at walking, jumping and fluttering among big boulders, and a group under watch can soon vanish by moving largely out of sight behind rocks.
In the breeding season, Scottish ptarmigan spend most of the daytime within 3m of the nearest rocks.50 By hiding among rocks, they reduce the risk of attack from predators, as do white-tailed ptarmigan.51 Although cover can take the form of one boulder or a few, it often comprises boulder lobes, scree, edges of boulder fields, rock outcrops or cliffs, and sometimes ridges or hillocks. Hens with downy chicks avoid large interlocking boulders where food is scarce and chicks could fall down deep holes. Once fully grown, however, ptarmigan often fly to such boulders to rest and preen in safety.
Densities of ptarmigan in Scotland are high on fine-grained mosaics of abundant food and boulders. Expanses of food plants without boulders usually support no territorial birds, the sole exception being when smaller features provide cover that allows a few to breed on ground without boulders, such as earth hummocks caused by freeze-thaw action.
Climatic effects on habitat
Across Eurasia and Arctic America, the upper altitude for plants that are eaten by ptarmigan sets the upper altitude to which they feed and breed. On many American mountains, however, the smaller, closely related white-tailed ptarmigan occupies the zone uphill. This keeps the rock ptarmigan’s upper limit there to a lower altitude than it would otherwise be. On steep slopes, the birds’ lower limit can be an abrupt line, where short vegetation with many rocks changes downhill to taller vegetation with few or no rocks. Below this line, Lagopus lagopus take over.
FIG 37. Scottish ptarmigan hen with foraging chicks. They are in vegetation beside small surface boulders that provide cover but do not have any dangerously deep holes. (Stuart Rae)
FIG 38. Lowest altitude (m) frequented by breeding rock ptarmigan. It rises towards the south, coinciding with the lowest altitude of prostrate vegetation. Red circles represent the Kuriles and Amchitka Island, two areas with exceptionally cold windy summers for their low latitude, and hence prostrate vegetation at low altitude. Blue diamonds represent five Scottish areas, illustrating how increasing windiness causes the lowest limit for prostrate vegetation to be closer to sea-level. Two of the black diamonds are the Norwegian islands of Lyngen and Lofoten, areas with lowest limits of prostrate vegetation that are unusually far up the mountains, in association with fairly mild summers for such high latitudes, owing to the Gulf Stream. They and central Alaska are the only areas on this graph that have willow ptarmigan, which push up the lowest altitudinal limits of ptarmigan (as in Scotland with red grouse), though this is not obvious from these data.55
The prostrate Alpine vegetation used by ptarmigan signifies cool summers, and it occurs at lower altitudes as one goes north. Its lower limit can differ at a similar latitude, however, where summers are colder or windier than is usual for that latitude.
Summer habitat in Scotland
Much high ground in Scotland has few or no food plants used by ptarmigan because of the presence of boulder fields, bare soil or grassland.52 For these reasons and the plants’ slow growth, bird densities are generally below those of red grouse on moorland. Prostrate heather or mountain azalea with few boulders typifies poor habitat, while blaeberry-rich vegetation with colluvial topsoil and more boulders is good habitat.
Ptarmigan and red grouse overlap in altitude – for example, by 300m in the Cairngorms – but they seldom overlap in habitat. Red grouse nest in tall heather with few or no boulders, while ptarmigan prefer a more varied short heath with many boulders.53 On ground occupied by ptarmigan, a patch of fairly tall heather may hold an isolated pair of red grouse or, more often, an unmated cock. On lower slopes occupied by red grouse, one may similarly find a ptarmigan pair or cock on an isolated patch of blaeberry with rocks.
Where coastal land is exposed to winds from a cool sea, Alpine vegetation extends to a lower altitude than in the more continental interior, in a gradient from inland eastern Scotland towards the northwest coast.54 The lower limit of ptarmigan with nests or downy chicks coincides with this, being highest on the relatively continental Lochnagar and lowest on the most oceanic hills of northwest Sutherland (Fig. 38).
Upper recorded limits for Scottish breeding birds lie just short of the highest summits in a given region, and rarely exceed 1,250m, except occasionally in late summer when families with fully grown young sometimes move uphill to eat plants on the loftiest tops. Maximum densities occur below 1,100m, where food plants are more abundant and productive than higher up.56 Scottish birds breed on suitable habitat whatever the altitude or aspect.57 Territories and nests are on short, freely drained heath, whereas hens with chicks prefer wet soils on flushes and snow-patch hollows. They have a more catholic choice once the young are bigger, when they also exploit berries and plants at high altitude.
Summer habitat outside Scotland
Although rock ptarmigan breed on low ground in the Arctic, they are absent from large tracts of flat wet tundra at or near sea-level, as on some parts of mainland Russia adjacent to the Arctic Ocean,58 around the Mackenzie and Yukon deltas, and along the Foxe Basin coast of Baffin Island.59 These areas support willow ptarmigan instead. On relatively flat land broken by rocky outcrops, such as southwest Baffin Island and the Ungava Peninsula, the two species breed very near one another, with rock ptarmigan on stony or rocky slopes and ridges, and willow ptarmigan nearby on flat wet tundra only a few metres lower.60
In some countries such as Greenland and Iceland, which have no willow ptarmigan, rock ptarmigan breed in birch-willow scrub,61 as well as in rocky habitats with short vegetation. In Iceland, much low ground supports tall heath with occasional scrub. Hrisey, an island with the highest recorded ptarmigan density in Iceland, is dominated by thick crowberry and heather62 with hardly any boulders, and hens nest in this heath vegetation (Fig. 39). In fact, this is a typical habitat for willow ptarmigan, and at a distance it resembles a British moor. Japan, most of the Aleutians, the Alps and the Pyrenees are also without Lagopus lagopus, and here rock ptarmigan frequently use tall vegetation.63 So, when relieved from competition with willow ptarmigan, rock ptarmigan use habitats that would otherwise be the preserve of willow ptarmigan.
Habitat in autumn and winter
In Alaska, rock ptarmigan in autumn keep to higher, more open ground than willow ptarmigan, which favour lower slopes and valley bottoms with tall willow thickets.64 In winter, however, when deep snow covers most ground vegetation, both often occupy the same habitat, though they take almost completely different diets (see below). Again in British Columbia, Norway and Scotland, rock ptarmigan in winter tend to stick to higher, rockier ground than Lagopus lagopus. But on stormy days with deep snow in Scotland, both species sometimes haunt the same ground in separate packs, well below the lowest places used by rock ptarmigan in summer.65 Even so, most ptarmigan are found higher up, in more exposed conditions than most red grouse.
FIG 39. Pair of rock ptarmigan on moor-like habitat on Hrisey, Iceland. (Adam Watson)
FIG 40. Ptarmigan flock on the Cairnwell in snow. Three birds are feeding, one is preening and seven are resting in the middle of the day. (Stuart Rae)
DIET
Winter
Unlike the ptarmigan’s varied autumn diet, which includes energy-rich berries and seeds, its winter fare comprises buds, leaves and stalks of woody shrubs, with little protein and much fibre.66 The birds are selective, however, taking food that contains more protein and phosphorus, and less fibre, than that generally available.67
The winter diet in Scotland comprises mostly leaves and shoots of crowberry and, to a lesser extent, heather and the green stalk tips of blaeberry, with smaller amounts of least willow and cowberry.68 When deep snow and storms force ptarmigan down to upper moorland, heather becomes their main food.
The birds eat many twigs and buds of willow and also some birch in Greenland and Iceland, two countries without willow ptarmigan.69 Amchitka in the Aleutians also has only rock ptarmigan, but willow and birch are scarce here. Crowberry dominates the vegetation, and it and horsetail form the rock ptarmigan’s main food source.70
Where both rock and willow ptarmigan occur in the same area, willow ptarmigan eat mostly willow scrub if available, whereas rock ptarmigan feed much on birch. Hence rock ptarmigan worldwide eat much birch, though taking much willow scrub in regions that lack willow ptarmigan. In Scotland, overgrazing by sheep and deer has almost eliminated such scrub. Hence the winter diet of ptarmigan here is probably poorer than before 1800, when fewer deer and sheep grazed our high hills.
Paul Gelting found that Greenland birds take some horsetail stems and reproductive capsules, both of which are quite rich in protein.71 Although they feed mostly on buds and shoots of polar willow, the birds will also eat many leaves of mountain avens, and buds and stems of purple saxifrage. All three of these plant species are quite nutritious, and are widespread in the Arctic on exposed ground where winds blow most snow away. During midwinter noon in Greenland, ptarmigan eat larger pieces of polar willow, well illustrated in Gelting’s photographs, thus filling their crops quickly. Gelting counted 9,100 items inside the average crop in early and mid-January.
Spring, summer and autumn
In spring, Scottish adults continue to feed on crowberry (Fig. 41), blaeberry and heather, but enrich their diet with early growing plants such as cotton-grass shoots and new leaves of chickweed or mouse-ear. Their diet on fertile hills includes more blaeberry and herbs than on infertile hills, reflecting the greater abundance of these richer foods.72 In spring on Hrisey in Iceland, the earliest plant growth occurs in agricultural fields beside houses, and foraging ptarmigan flocks concentrate in such locations (Fig. 42).
In summer, adult ptarmigan eat a variety of herb leaves, flowers and moss capsules, as well as shoots of crowberry, blaeberry and least willow. Chicks eat plants on their first day out of the nest, but also many insects in their first two weeks. In the subarctic and Arctic they favour the bulbils and spikes of Alpine bistort, which contain 20-22 per cent protein,73 roughly equivalent to the level found in commercial feed crumbs for poultry chicks. This plant abounds on moist soils in hollows, and though it is mostly covered in snow in winter it becomes available at the thaw. Though Alpine bistort is far scarcer on British and Irish Alpine land and moorland, it grows locally on rich moist soils such as on the Cairnwell, where sheep have been seen eating it.74 Overgrazing has doubtless contributed to its scarcity in Britain.
The autumn diet of ptarmigan in Scotland comprises many berries, seeds of grass, sedge, rush and wood-rush, and shoots and leaves of least willow, as well as the flowers and shoots of heath species. In the Arctic, autumn snowfalls seal off much vegetation and frost preserves the berries. During the spring thaw, the berries are a palatable, surprisingly abundant food, rich in energy for bird and
FIG 41. Crowberry, the main food of Scottish ptarmigan, with a setter dog pointing at a nesting hen. (Adam Watson)
FIG 42. Flock of Icelandic rock ptarmigan foraging in a hayfield on Hrisey in spring. (Adam Watson)
human alike, and rock and willow ptarmigan eat them. Such preservation occurs too rarely in Scotland to be valuable in spring. Seldom does late-autumn snow lie long, so birds and other herbivores consume almost all berries before winter. Occasionally, ptarmigan eat some crowberries in spring, which being less palatable than blaeberries are more likely to survive the winter.
METABOLISM
Winter
For rock, willow and white-tailed ptarmigan, food is readily available in winter, and they can store a meal in their crop and digest it at leisure overnight. Rock ptarmigan spend much time resting in sheltered places, often in sunshine. Studies of white-tailed ptarmigan reveal similar behaviour and a low expenditure of energy.75 In central Alaska, where winter daytime temperatures commonly sink below -20°C, rock ptarmigan spend much of the day under snow, white-tailed more so and willow ptarmigan less so.76
Of special interest is the Svalbard ptarmigan. Other rock ptarmigan at about 80°N in Greenland and Ellesmere Island migrate south for the darkest time of the year, without a sea crossing or with only a short one. Svalbard ptarmigan, however, would have to fly 1,000km south to reach Norway, a risky journey. Instead, they remain resident on the island, and have evolved impressive adaptations to cope with the risks of wintering so far north.77 The Gulf Stream passes the west side of Svalbard, keeping the sea open and the climate milder than is usual for such a high latitude. Rain can fall in winter and subsequently freezes, sealing off food. To cope with such icy periods, birds fatten in autumn, a time of plentiful nutritious food. Cocks at this time weigh up to 1.2kg and fat comprises up to 35 per cent of their body-weight. Captive birds achieve these proportions despite eating less,78 and presumably conserve energy by spending more time resting. Wild birds are almost fat-free by February, when the first daylight appears again.
Summer
When an incubating hen ptarmigan returns to her cool eggs after a feeding trip, she increases her heart rate and rapidly pumps blood to her incubation patch.79 Even so, cold wind, fog, rain or snow showers often prevail in early summer, so it may be wondered how the tiny chicks survive. Chicks of Alaskan rock ptarmigan that are only five days old can maintain normal body temperature for 20 minutes at an ambient temperature of 10°C, whereas Norwegian willow ptarmigan cannot achieve this until they reach ten days.80 Alaskan chicks need to forage for only six minutes per hour, and week-old young can produce about three times as much heat, presumably by shivering, as do willow ptarmigan of the same age.
Despite their smaller size, the downy rock ptarmigan chicks are better adapted to cold than their willow ptarmigan brethren. The same applies throughout their life. They are thus better able to cope with more snow, rain, fog, cold and wind, and less shelter, than can be tolerated by willow ptarmigan. Nevertheless, even slight worsening of weather in the Swiss Alps reduces the feeding periods of downy chicks.81 Prolonged heavy snow or rain during daytime, especially in strong winds, can cause heavy losses, such as in Iceland during a July snowstorm even though chicks were a month old.82 Very few downy chicks survive heavy snowfalls on the Cairngorms, and more than half the young died during heavy rain in 1990 even at much lower altitudes on the Cairnwell.83
Ptarmigan can be too hot on warm summer days, however, and either seek shade from rocks or sit in water or snow. In hot sunshine, they and Lagopus lagopus pant rapidly with bills open, to lose heat quickly.
MOVEMENTS
Seasonal movements or migration
In southerly countries where ptarmigan are winter residents, such as Scotland, birds often stay on the same hill throughout the year. In northernmost Canada, Alaska, Greenland and mainland Russia, however, many move south in autumn and north in spring, some flying along the coast or over the sea.84 On the north coast of Baffin Island, they arrive in early October from Bylot Island, ‘in many cases so tired by the flight that they alight on the beach almost exhausted’.85 Some occur ‘regularly in winter as far north as Thule’ in Greenland,86 and in Baffin Island. None the less, many move south in both islands, and thousands from Baffin Island arrive in autumn on the coasts of the Ungava Peninsula and Labrador, and in spring in Labrador as they fly north again.87 Ptarmigan can be intrepid explorers, as exemplified by fresh tracks found in June at 1,600m on the expansive Penny Icecap of Baffin Island.88
Seasonal movements of up to 500km have been reported in northern Russia and more than 1,000km in America,89 and a bird ringed on Disko Island in Greenland during July was recovered the following February more than 1,000km to the south.90 The east Greenland race has ‘repeatedly been taken in winter at sea and in Iceland’, as proved by the gizzards of birds shot in volcanic Iceland containing grit from the non-volcanic rock of Greenland.91 Large-scale movements in Greenland coincide with peak numbers, and so may involve density-dependent emigration (see Chapters 3 and 14).
The timing of autumn movement in America is irregular, associated with seasonal snowfall. Canadian rock ptarmigan are far less migratory than willow ptarmigan, tending to concentrate in the southern part of the breeding range.92 Each species occurs in winter further south than its southern breeding limit, but willow ptarmigan go much further beyond this than do rock ptarmigan.93
Many male rock ptarmigan in Iceland and Alaska remain in northern parts, whereas hens move to more southerly regions.94 Presumably it is beneficial for old cocks to stay near their former territories, so that they can occupy them quickly in spring. They return to their breeding grounds on the Icelandic island of Hrisey and at Windy Lake in Canada’s Northwest Territories two to three weeks before hens,95 and earlier than hens in Greenland, Alaska and the Swiss Alps.96 In Svalbard and Canada, old territorial cocks returning to the breeding grounds after being away for the winter appear in their former locations.97 In contrast, although returning hens do come to the same general area, they often choose different territories and cocks.
Youngsters disperse in autumn when broods break up. In the far north, some move far – in Iceland, for example, up to nearly 300km from where they were ringed as chicks.98 Such movement of young presumably involves seasonal migrations of the kind observed in many old birds there, plus natal dispersal of young to breed in places away from where they hatched.
Short movements to food in summer and autumn
Ptarmigan often move locally to food. During summer in Greenland, hens with chicks visit moist hollows, often near small snow patches. These sites have less bare ground than usual, because continual irrigation prevents them from drying out. As a result, they support abundant willow, herbs and Alpine bistort, all of which are good chick foods. Several ptarmigan families in Greenland were seen to concentrate at former human settlements,99 where faeces, urine and food waste from people and dogs had enriched the soil.100
After hatching, Scottish hens walk with their broods to flushes that support abundant invertebrates, a rich food for chicks. Later, when the chicks are partly feathered and eating mostly plants, many families visit snow patches. There, plants newly freed from the snow and in the first flush of growth are more nutritious than those of the same species that grew earlier in the summer on less snowy ground.
Many Scottish adults and well-grown young move uphill to higher, more barren ground in late July and August, where they feed much on plentiful least willow, and others move to eat berries at places with good crops. In the Swiss Alps they also go uphill in late summer, as high as 3,000m. The cocks go first and hens with broods move later, the birds returning to the breeding grounds when snow deepens at high altitude.101 Many birds in Iceland leave the lowland breeding grounds in late summer and move into mountains above 600m.102
Short movements to food in winter
In the Cairngorms, Seton Gordon watched ptarmigan moving downhill on wing and foot at the onset of a severe snowstorm and gale, and shortly afterwards they came back up again into a relatively sheltered corrie when conditions on the lower slopes had become even worse.103 In stormy weather, packs of birds often fly to sheltered places for feeding,104 and a big movement was witnessed in Norway during a blizzard.105
Many ptarmigan move downhill during early winter in deep snow in the Pyrenees, going down to scrub or birchwood.106 Scottish birds avoid the loftiest exposed land, although they will stay even as high as 1,100m if the ground remains largely snow-free. When hard-packed snow, hoar frost and rime cover the highest ground, however, packs concentrate on Alpine land below 900m. If snow or ice covers plants there, too, the birds fly to areas of high moorland where some heather projects above the snow. There they often overlap with red grouse, although most grouse in such conditions move yet lower.
On the other hand, when deep snow blankets almost all higher moorland and lower Alpine land in the Cairngorms, ptarmigan move uphill on days without gales. There they eat heath plants on exposed ridges where wind has blown most of the snow away. In east Greenland, too, they move to exposed places where plants are snow-free.
The sexes sometimes separate by altitude, cocks in the Cairngorms staying on their territories on largely snow-covered ground more often than hens.107 In Iceland, adults in winter flocks tend to dominate juveniles, and wintering juveniles often stay in separate groups from adults, eating different vegetation.108
AVERAGE POPULATION DENSITIES
The average density of rock ptarmigan tends to be high where their preferred food plants are abundant, as in Scotland, in combination with physical cover from rocks.109 In contrast, the Canadian high Arctic has low densities of ptarmigan and very little vegetation at all, let alone ptarmigan foods, and plant production is also very low (see Table 6).
FIG 43. Lower-altitude ptarmigan habitat on rich soil with boulder cover and abundant food plants (Cairnwell). (Stuart Rae)
FIG 44. Higher-altitude ptarmigan habitat on poorer soil with boulder cover but sparse food plants (Ben Macdui). The big difference between this example and Figure 43 arises from the combination of two factors: altitude and bedrock. (Stuart Rae)
In Scotland, food plants are less abundant at higher altitudes owing to the more severe climate and hence poorer soils. In addition, average rock ptarmigan densities on different hills at the same altitude are associated with different underlying bedrock and associated soil fertility. When the effects of altitude and soil fertility are combined, they can affect average densities greatly (Figs 43 & 44). Thus, the average density of cocks and hens on base-rich rocks at the lower-altitude Cairnwell and Meall Odhar has been 48 cocks and 45 hens per km2, whereas on acidic granite at the higher-altitude Derry Cairngorm it has been only 18 cocks and 16 hens per km2.110
Year-to-year fluctuations in density
Ptarmigan numbers vary greatly in different years (Table 12) and some long series of counts show evidence of cycles.111 The number of shot ptarmigan exported from Iceland over many decades fluctuated in a ten-year cycle, and bags in three provinces of the Italian Alps and in a Swiss canton showed weak cycles.112 Bags are less reliable than counts, however, and the Italian and Swiss bags were too short term to draw firm conclusions about cyclicity. Counts in Alaska and Canada suggest that ten-year cycles are likely,113 but the evidence is insufficient to be sure. In one documented case on the Cairngorms, a ten-year cycle was correlated with a cycle in June air temperature.114 At the base-rich Cairnwell and Meall Odhar 20km to the south, however, the more erratic fluctuations in numbers were associated with a different and more erratic weather feature: spring snow-lie (see Chapter 14).
At Alaska’s Eagle Creek and in Scotland, the only areas where population studies of both sexes have lasted beyond a few years, the recruitment of young to the spring population is the demographic factor that accounts best for the change in adult numbers since the previous spring.115 The recruitment rate rises as the population increases from a trough, but falls off rapidly towards the peak and remains low during the decline. In Scotland and Svalbard, cocks have been found to limit their spring numbers through territorial behaviour (see Chapter 9).116 This may involve aggressive behaviour that limits the recruitment of young, as in red grouse, but has not been studied.
SURVIVAL
Some information on survival of rock ptarmigan has come from marking adults on an area in one summer and noting those that return the following summer.117 Such ‘return rates’ are often used as a surrogate for survival. Data from several countries, including Scotland, centre around 47-8 per cent (Table 13).
TABLE 12. Some peak and trough numbers per km2 during spring (cocks, hens) in studies of rock ptarmigan that lasted long enough to justify references to ‘peak’ and ‘trough’. Table 6 includes the data below, in greatly summarised form.
Notes
Counts in successive years have been carried out at Svalbard, Sarcpa Lake and Windy Lake (references in Table 13), Japan (Soichiro et al., 1969), Russia (reviewed by Potapov, 1985), Ungava (Olpinski, 1986) and Lombardy (Scherini et al., 2003), but data cover too few years to show peaks or troughs reliably.
# The peak at the Cairnwell was 75, 65 (Watson, unpublished).
TABLE 13. Percentage of adult rock ptarmigan marked in one summer that returned to a delimited study area in the next summer (return rate).
Notes
Bergerud (1988) gave a 44 per cent annual survival for hens at Eagle Creek, using data in Weeden & Theberge (1972), and 54 per cent for hens on Hrisey, using data in Gardarsson (1971). These values were estimated from counts, and so are not return rates.
# This is such a low value that emigration to ground outside the study area is likely.
The converse of survival is mortality, and the converse of return rate is loss from the study area. Such loss consists of mortality plus net movement out of the area, possibly to breed elsewhere. There are few reliable data on survival or mortality, so it is safer to refer to return rate or loss.
Summer losses118 at Alaska’s Eagle Creek and Scotland’s Derry Cairngorm were low, at around 10-15 per cent, and at the Cairnwell they were slightly higher.119 This probably overestimated summer mortality in Scotland, because temporary movement out of the relatively small study areas caused a high proportion of summer ‘loss’, especially at the smallest study area, at the Cairnwell. Summer losses of marked birds at Canada’s Windy Lake averaged about 20 per cent for each sex, nearly all taken by falcons.120 On Hrisey, Iceland, more cocks than hens were lost in early summer, when gyrfalcons killed conspicuous white cocks on prominent lookouts.121 A study of prey taken to gyrfalcon nests near Húsavík, Iceland, confirmed the excess of cocks taken in April-June, but in July the falcons brought more hens than cocks, resulting in similar losses of both sexes over the season as a whole.122
Losses in winter (actually measured from late July through to May) exceeded those in summer at all areas where it was estimated.123 At Derry Cairngorm and the Cairnwell, winter losses in both sexes averaged 30-44 per cent of adults and first-year birds combined, tending to be greater after summers with good breeding.
There is little evidence on longevity, because few studies with marked birds have lasted long, and birds may move outside study areas and yet still be alive. However, there are Canadian records of two cocks living at least four and five years, and two hens living five and seven years.124 An annual survival rate of 50 per cent would leave 6 per cent of adults alive at five years of age.
NUMBER OF HENS PAIRED WITH COCKS
Most cocks pair with a hen each and some pair with two, while others are unmated. One cock had three hens for the summer on Victoria Island, Canada, and at Sarcpa Lake a few cocks had three each and one had four.125 In Scotland, two hens occasionally breed with a cock, but incidences of mating with more than two have not been recorded.
Territorial cocks outnumbered hens in years of population decline on Derry Cairngorm, but in years of increase the ratio was about one cock per hen.126 On average, the male excess here exceeded that at the Cairnwell, where 1.5 cocks per hen was the highest figure, compared with 2.0 on Derry Cairngorm. The base-rich Cairnwell has food plants that contain higher levels of protein and phosphorus than those at Derry Cairngorm. As in red grouse, large excesses of cocks are often associated with poor food quality, especially during cyclic declines.
At Derry Cairngorm, ‘Though there were enough hens in February/early March to pair with all the cocks that had territories then, half of the cocks finally remained unmated’.127 Many hens vanished suddenly in spring, such as 21 within five days in early March 1952, and 22 within ten days in March 1954, but none was found dead then, so it was concluded that they moved out. Perhaps they went to hills with lower or increasing densities.
A preponderance of territorial cocks during the nesting season has been recorded in several countries.128 At Hrisey in Iceland, however, the sex ratio in early spring was about 1:1, but gyrfalcons then killed far more cocks than hens, resulting in many unpaired semi-promiscuous hens.129 In a two-year study on the Ungava Peninsula, Quebec, the ratio before pair formation was again near 1:1, but although many territorial cocks later had one or more hens, many remained unpaired.130 Similarly, in a short study at Sarcpa Lake some cocks had one or more hens, while others remained unpaired.131 Heterogeneous habitat occurred at both areas, including poorer ground perhaps suitable for unmated cocks but not for breeding hens. At Ungava the territories of unpaired cocks were so small (see Table 21) that they may have been inadequate for hens.
Reasons for differences in the sex ratio
Because gyrfalcons took more cocks than hens on Hrisey in spring, it was claimed that the excess of breeding cocks in Scotland and other southern countries might result from their ‘unbalanced’ predator situation, with no gyrfalcons killing the cock ptarmigan.132 In two summers at Windy Lake, however, 48 territorial cocks were paired with 49 hens, and ten more territorial cocks remained unmated, despite one of the highest known nesting densities of gyrfalcons in the world, and falcons took cocks and hens equally.133 Also, as explained above, the sex ratio in early spring was balanced (1:1) on Derry Cairngorm. In years when the area had a large excess of cocks in the nesting season, this unbalanced ratio occurred because more hens than cocks had left. Hence the claim that ‘unbalanced’ sex ratios are caused by predators taking more hens than cocks seems unlikely.134
The greater frequency of unmated cocks in Scotland is associated with poorer diet. Overgrazing sheep and deer have almost eliminated scrub of willow and birch, and continue to remove Alpine bistort and most cotton-grass shoots. This is exacerbated by the low content of protein and phosphorus in food plants on infertile soils. Thus the average percentage of unmated cocks on the infertile granite of Derry Cairngorm exceeds that on the base-rich rocks at the Cairnwell and Meall Odhar. The unmated cocks’ small territories may be inadequate to support breeding hens, which leave, perhaps in search of better food or less crowded areas with a lower population density.
DATE OF EGG-LAYING
Longer days induce egg development, but the response by local populations to the same day length varies with climate. For example, hens in north Canada lay in June, several weeks later than in the much less snowy Iceland at the same latitude. Many high-Arctic hens do not lay until late June135 and some not until early July.
Another enlightening comparison is that between Amchitka, in the Aleutian islands, and Scotland. Amchitka lies as far south as London, but here the hens’ increase in weight before egg-laying comes weeks later than in the Cairngorms, peaking in June when they lay eggs.136 Cocks on Amchitka establish territories in early May, months later than birds in the Cairngorms. Their testes reach peak size in early June, and the hens’ ovarian follicles reach peak size in late June. Hatching on Amchitka also comes one to three weeks later than at Eagle Creek in central Alaska, 1,600km further north.137 Though oceanic Amchitka has mild winters, summer comes late and breeding follows suit.
Within a given region, hens fine-tune their response to climatic conditions by laying eggs earlier in springs that are warmer than usual. In such springs, fresh growth by plants supplies the rich food that hens need for producing eggs of high quality. In the Cairngorms, the earliest hen at low altitude in a mild, snow-free spring lays her first egg at the end of April, and the latest hen at high altitude in a snowy year does not lay until the end of June. At a given altitude, the date of laying varies from year to year in relation to May temperature, with early eggs in warm Mays, when plants grow early. The date of hatching is related to the date when blaeberry begins to grow, thus linking hatching date to diet and weather.138
In the Swiss Alps, some paired hens did not seem to breed in a summer with ten days of snowfall in late June.139 Since hens usually nest in mid-June, they may perhaps have nested and then deserted. Heavy snowfalls cause many Scottish hens to desert, and this can be readily overlooked unless several visits are made during and immediately after the snowfall.
In a given year or area, some hens lay earlier than others at the same altitude or aspect. On Svalbard and the Cairnwell, heavy hens lay earlier than light hens,140 presumably because they are in better condition at the point of lay. We think it likely that high-quality hens pair with cocks that have big territories offering good food, and good food in turn helps induce early laying.
NESTS, EGG-LAYING AND INCUBATION
Rock ptarmigan hens nest in their first year of life. Although less is known about them than Lagopus lagopus, the evidence indicates that all hens nest each year. They choose the nest site, and make a shallow scrape in the ground or vegetation, lining it with plant litter and the odd loose feather.
By far the commonest nest site for a Scottish hen is short vegetation beside a boulder (Fig. 45), where the upper half of her body rises above the vegetation but the boulder provides cover, a cryptic background, and shelter. There she relies on her camouflaged plumage to avoid being seen by predators. Only exceptionally does she nest in tall vegetation, though one hen on Derry Cairngorm was overhung by a small patch of heather 25cm tall.141 Another unusual nest there lay under an overhanging rock shelf that kept rain off the hen and eggs, and mostly hid them from the view of predators.142
On average, a Scottish hen lays one egg about every 1.5 days.143 After laying, she usually covers her eggs with plant litter before leaving the nest, thus hiding them from predators and insulating them from frost, falling snow and cold rain. Even partly covered eggs are remarkably difficult to see, and the litter may also reduce scent from the eggs.
FIG 45. Ptarmigan hen on a nest in short vegetation beside a boulder – a typical Scottish site. The blaeberry shoots around the nest are just beginning to grow. (Stuart Rae)
CLUTCH SIZE
Average clutch sizes in different areas
Ptarmigan in Scotland lay smaller clutches than red grouse in the same region – roughly an egg fewer. Clutch size varies greatly between different countries, although the difference is not related to latitude – for example, clutches on Svalbard differ little from those in Scotland (Table 14).
TABLE 14. Mean clutch size, number of chicks per hen and brood size (number per hen with a brood) of rock ptarmigan, in order from north to south. Chicks# were eight days old at Ungava, ten days at Windy Lake, three to four weeks at Hrisey, four to eight weeks at Svalbard and fully grown elsewhere.
Notes
Because breeding success varies during population fluctuations, only the Icelandic, Alaskan and Scottish studies lasted long enough to show reliable averages. Alaska and the Italian Alps are poorer for nutritious plants than Hrisey.
# Studies of chicks aged up to eight weeks lacked later observations. At Hrisey, gyrfalcons killed chicks from late July, when they were about four weeks old. Near Húsavík, almost a quarter of chicks in mid-July were killed by the end of August (Nielsen, 2003). If one allows for this, breeding success at Hrisey estimated as full-grown chicks would still be very good, but differences from Alaska, Scotland and Italy would be less than above.
* After Weeden & Theberge (1972), using the same years as Weeden (1965a).
Ptarmigan in Arctic Canada eat nutritious willow and lay big clutches, whereas Scottish birds depend mainly on heath species of poorer feeding value and lay small clutches. In the weeks before hens lay in Scotland and other countries, they supplement their main diet with newly growing herbs, which are far more nutritious than heath species. In Scotland they have to compete for this relatively scarce food with the large mouths of many hungry red deer and often sheep also. In conclusion, the average clutch size depends more upon food quality than latitude.
Clutch sizes of individuals
A hen’s condition influences her clutch size in a given year. In studies at Svalbard and the Cairnwell, heavy hens laid larger clutches than light hens.144 Probably the amount and nutritional value of food on the cock’s territory influences her weight and condition before she lays.
On a given area, the average clutch size varies from year to year. For example, hens on Derry Cairngorm laid larger clutches after mild springs with early plant growth.145 They also laid larger clutches in years of rising population than during population declines. On Hrisey, the average clutch size was related inversely to adult density, so that hens at low density produced large clutches. The Hrisey study did not last long enough to check reliably whether clutch size varies with the phase of the fluctuation as at Derry Cairngorm.
Among hens that lose their first clutch to predators or to desertion in snowstorms, some lay a repeat clutch with three to four fewer eggs, resulting in a later set of young. In Scotland these late broods contain young that are about five to six weeks old at the end of July – approximately half-grown when the young from successful early broods appear almost as big as their mothers.
BREEDING SUCCESS
This is the number of young reared per hen. It equals brood size (the number of young reared per brood) in years when no hens fail. In most years, however, it is less, because some hens rear no young. Many hens fail in some years: at Derry Cairngorm mostly due to entire broods dying, on Svalbard to hens deserting nests in snowfalls, and at Cairn Gorm to crows robbing nests.146 In extreme cases at Derry Cairngorm, all hens reared young in two years, and none in two other years.147 Breeding success varies amongst Scottish areas, and amongst countries. The study area with poorest breeding is Derry Cairngorm, slightly better on more fertile soils at the Cairnwell and Meall Odhar, and successively better in Lombardy, Eagle Creek, Svalbard, northern Canada and Hrisey (see Table 14).
Most deaths of Scottish chicks occur in their first week, and breeding success depends mainly on chick loss. The hatchlings’ viability partly determines their mortality. Viability depends on egg quality, which in turn is influenced by the diet of laying hens, especially the amount of nutritious new plant growth available to them.148 The quality of the hens’ diet on the relatively fertile Cairnwell and Meall Odhar exceeds that on Derry Cairngorm, and chick survival usually reflects this.
Chick survival is also influenced by the amount and quality of their food, by predators and by weather. Sheep and red deer in Scotland have eliminated almost all willow scrub, and remove other nutritious foods such as Alpine bistort and cotton-grass shoots. This reduces food quality for hens and chicks, and explains poorer breeding here than in countries further north.
In Iceland, for example, hens have a good diet in spring149 and summer. Chicks on Hrisey eat Alpine bistort, a plant so nutritious that they do not need insects to boost their intake of protein, and in most years they survive well. Subsequently, families flock to forage on old hayfields, where agriculture would have improved soils and resulted in the growth of nutritious plants.
On any one area, some hens do better than others. In studies at Svalbard and the Cairnwell, heavy hens reared bigger broods than light hens, and likewise early-laying hens reared bigger broods than late-laying hens.150 Svalbard hens that hatched their eggs outweighed hens that deserted their nests or lost them to predators. First-year Svalbard hens increased their weight later than older hens, laid smaller clutches and reared smaller broods. In short, the hens’ condition affects their later breeding success.
ENEMIES
Northern native people kill many rock ptarmigan for food, but vast areas of the bird’s range are uninhabited by humans. Large numbers have been shot by sport-hunters in Russia and Iceland, with fewer taken in other countries, including Scotland. In many southern countries, man has eliminated some predators such as wolves and wolverines. This, along with the human-induced rise in the number of carcasses of sheep and deer, and increased food refuse, has led to an increase of foxes in Britain. Arctic foxes that were unwisely introduced to several Aleutian islands have extirpated ptarmigan there.151
Foxes, now the main predator on Scottish ptarmigan, take adults, eggs and chicks, as do stoats and weasels, although to a far lesser extent. Next to the fox, golden eagles kill many adults and chicks, and some adults fall prey to peregrines. Hen harriers and short-eared owls occur too rarely and briefly to be of any importance, and in several years a snowy owl on Cairn Gorm plateau has fed largely on ptarmigan adults and chicks.152 Near the very few gulleries at high lochs, common gulls take some eggs and chicks locally.
Data on the numbers of ptarmigan taken by different predators have been published from Scotland and elsewhere.153 During a study on Derry Cairngorm, for example, foxes and golden eagles killed 62 adults, and only two others were found dead without signs of injury and in poor condition. Crows, though normally resident far below Alpine land, were attracted by food scraps at a busy tourist development on Cairn Gorm, and took ptarmigan eggs and chicks.154 Following these losses, combined with deaths on ski-lift wires, no ptarmigan summered on the most heavily developed part of the area for many years.
Compared with red grouse, relatively few parasites live on and in Scottish ptarmigan, but they include the threadworms that kill some red grouse. In most ptarmigan these are absent or occur in small numbers, and so are not sufficient to cause ptarmigan declines.155 In Scotland, ticks have not been recorded on ptarmigan or on ptarmigan ground. This may alter with climate change.
THE FUTURE
Threats to ptarmigan include more wires, disturbance by people and dogs near roads, extra crows induced by human activities, habitat loss from ski development, and pollution and climate change. Overgrazing by sheep and deer has reduced heath and extirpated ptarmigan on otherwise suitable rocky hills in Scotland, England, Wales and Ireland. An end to sheep subsidies and to deer overpopulation could bring ptarmigan back.
SUMMARY
Ptarmigan have a circumpolar Arctic distribution with southern extensions on islands and mountains. Their three plumages bestow good camouflage. Scottish birds reach high density on ground that has much food alongside boulders that provide cover. Scottish densities include the highest so far recorded, associated with abundant food, but the food is of low quality and results in generally poor breeding. Differences in the quality of the hens’ food from one year to another influence breeding success. Birds in Arctic Canada occur at very low density, associated with sparse food plants, but the food is of high quality, so they lay large clutches and breed well.