CHAPTER 3
Red Grouse and Willow Ptarmigan
RENOWNED FOR CENTURIES as a gamebird, the red grouse has an economic value that has led to much research, so it is one of the best known of animals. Ornithologists formerly regarded it as the sole bird species unique to Britain and Ireland, but for decades it has been considered a race of the circumpolar willow ptarmigan.1 In his book on grouse, Otto Höhn regarded it as halfway to a species,2 and species rank has again been proposed.3 In this chapter we discuss how red grouse and willow ptarmigan make use of vegetation as food and cover, and summarise their movements, fluctuations in numbers, survival and breeding success.
In its behaviour, the red grouse closely resembles the willow ptarmigan, but that bird has a white dress in winter and white wings at all seasons. After the last ice age, during a period when the climate of Britain and Ireland was warming, red grouse evolved a coloured plumage throughout the year, suiting the background of dark, usually snow-free moorland.
An unusual attraction of Britain and Ireland is heather moorland – millions of hectares of it. Here, the red grouse makes its home. The moors are impressive in all seasons, but especially so in August and September, when whole hillsides turn purple with millions of heather flowers. In the dark silence of early morning, the first grouse-cock crow at daybreak rings out the bird’s challenge as he proclaims his moorland territory. Then ‘the answer comes quick from the north, and within a couple of minutes the whole dark moorland re-echoes with wild music – an unrehearsed orchestra of Nature. What a concert!’4
‘Grouse-moor’ is moorland where grouse-shooting is the main land use. ‘Heather moorland’, where heather predominates, includes grouse-moor and also land where grouse are seldom or never shot. Both are valuable for other
FIG 11. Cock willow ptarmigan amongst willow in Alaska, showing spring plumage with a chestnut head and neck, and with a white face remaining from the winter. (Robert Moss)
wildlife, landscape and tourism. Heather and red grouse are virtually Scottish emblems, although some deplore them as romantic clichés.
The willow ptarmigan is a beautiful bird found in northern countries amid splendid scenery.5 Hunters seek it out in autumn, a time of spectacular colour as frost turns leaves yellow or crimson. Many biologists have studied willow ptarmigan, and this chapter touches on their work, although it is mainly about red grouse. When mentioning both birds together, we use Lagopus lagopus, the scientific name for the species.
THE BIRDS
Dimensions and plumage
Slightly smaller than a pheasant, the red grouse is about as long as a wood-pigeon but with a heavier body, and cocks are 5 per cent longer than hens.6 The dark brownish-black bill is stout, easily snapping off woody twigs as food. Adult cock red grouse weigh 600-690g, their lean point in March coinciding with vigorous territorial activity and courtship. Cocks outweigh hens in every month save March through May, when hens surpass them to reach some 670g in April, having fattened before laying eggs. In June and July, the hens, now thin after incubation, average 560g and cocks 660g.
Birds differ in size in different regions. Although red grouse have shorter bills and tails than willow ptarmigan in north Norway,7 they are heavier, and the heaviest ones weighed by us were caught on windy, fairly snow-free moors near the east coast of Scotland. Birds weigh less and have shorter wings in interior Alaska than near its windy coast. The smallest Russian birds live in the subalpine belt of the southern Siberian mountains, larger ones live in the taiga, yet larger ones are found on tundra, and the largest of all occur in southerly Kazakhstan, where winters are cold and windy with little snow.8 We infer from this that small races live in regions where deep, undrifted snow prevails in winter, affording good insulation for roosting. Rock ptarmigan also weigh less in such regions than on windy and often milder coasts.
A reddish-brown colour pervades the plumage of red grouse throughout the year and of willow ptarmigan in summer. Birds in west Scotland, Wales and Ireland are lighter coloured than those further east, their yellowish plumage suiting the paler background of the grassier moorland found in such regions. Willow ptarmigan in Kazakhstan are also slightly yellowish in summer, blending in with the background of dry forest-steppe.
FIG 12. Mean winter body-weight in grams of Lagopus lagopus and rock ptarmigan in relation to (a) latitude and (b) categories of deep undrifted snow in winter, from scarce (1) to widespread (4).9’10 Mean weight includes crop contents. In most cases we calculated it by adding together mean weights for young cocks, old cocks, young hens and old hens, and dividing the total by four, but in some cases a mean was published without specifying how it was obtained, or in one case a mean of all sex and age categories was given irrespective of their proportions in the sample.
Notes
1. The observation that northern animals of the same species tend to be larger is known as Bergmann’s rule. Northern climes are colder, and bigger animals have an advantage here in staying warm because of their smaller ratio of surface area (through which heat is lost) to body mass (in which heat is generated).
2. Willow and rock ptarmigan show this tendency only very weakly. Furthermore, willow ptarmigan are bigger than rock ptarmigan, although the latter generally live in conditions of greater wind-chill, and rock ptarmigan are bigger than white-tailed ptarmigan, which live in greater wind-chill than the other two species in the same region. This is associated with the observation (Robert Moss) that white-tailed ptarmigan spend more time under the snow than rock ptarmigan in the same area, and that rock ptarmigan spend more time under the snow than willow ptarmigan. We think that the insulation provided by snow-roosting allows ptarmigan to be smaller. Deep, undrifted powder snow provides better insulation than wind-packed snow, because it contains much more air (see Chapter 8). Hence, ptarmigan should be smaller where deep, undrifted powder snow is more widespread and consistently available. Being smaller would allow them to use shallower snow and so extend the area available to them. Another advantage of small size is that less food is needed. An advantage in itself, this might also result in less time being required for foraging, thereby allowing more time under the snow and thus less heat loss.
3. Data on latitude were taken from atlases and larger-scale maps. In most cases the exact location was known, but in a very few cases (such as north Greenland and Yakutia) it covered a band of latitude, in which case we took a mid-point. We used four categories as scores for the prevalence of deep, undrifted powder snow during the winter period in the various regions. This rested mainly upon published accounts by meteorologists, explorers and ecologists studying Lagopus, along with published photographs, and partly on personal experience of snow conditions by colleagues and ourselves.
4. Statistical analysis showed that variations in ptarmigan weight were explained better by the category of powder snow than by latitude. Because the ratio of the birds’ surface area to weight is about 2:3, we used weight raised to the power of 2/3 as the variable to be explained. Most of the variation in this aspect of weight was explained by analysis of covariance (R2 = 0.81). Explanatory variables were species (two categories, willow or rock ptarmigan), latitude (continuous) and snow category (continuous). Weight tended to increase with increasing latitude, but the effect was not significant (F1,49 = 1.02, P = 0.32). Weight declined with increasing powder snow (F1,49 = 102.5, P < 0.0001). Note that weights of rock and willow ptarmigan were similar in places where powder snow occurred rarely (category 1), but that the difference between the species increased in regions with more powder snow (categories 2-4). This suggests that differences in body-weight between the two species are due largely to differences in the way they use snow, such that rock ptarmigan in regions with deep powder spend more time under snow than willow ptarmigan. Thus, the analysis showed that the difference in weight between the two species was not significant (F1,49 = 1.76, P = 0.19), whereas the interaction between snow category and species’ weight was significant (F1,49 = 4.28, P = 0.0439). 5. One effect of snow on weight was that birds in regions with category 1 powder snow were 124g heavier than birds with category 4 powder snow. The SED (standard error of difference) between the mean weights of the two sets of birds was only 18g. Such a small SED relative to the large difference in mean weight signifies that the observed difference in weight was reliable.
FIG 13. Eggs in nests. Left to right, top to bottom: red grouse, ptarmigan, greyhen, capercaillie. (François Mougeot, Stuart Rae, Desmond Dugan, Desmond Dugan)
Eggs and chicks
The oval eggs of Lagopus lagopus, slightly larger than those of a wood-pigeon, are off-white with a tinge of pale brick red when newly laid, and are marked by many brownish-red blotches. As incubation proceeds, the blotches turn dark brown and the eggs shine with a strong gloss. Hatching takes about a day.
Down covers day-old chicks to their toenails, its colour varying from largely black with little yellow or brown, to predominantly yellow and chestnut. Brood mates have a similar colour, which also resembles the down colour of their parents as chicks, so the colour is inherited.11
A day after hatching, chicks leave the nest. They peck vigorously at insects or heather, and run to hide under vegetation if frightened. In Scotland, most chicks hatch in late May and appear full grown at 12 weeks, although old grouse still outweigh them in August and September.12 Chicks on Russian tundra put on weight much faster than this, and faster also than birds in forest-steppe. Chicks of Irish bogs are very slow-growing, and they also moult their chick primaries later than chicks at Kerloch in Deeside, Scotland.13 When eggs from an Irish bog were hatched in captivity and the young given a high-protein diet, their body-weight and chick primaries grew no faster. The reason for this is that fast growth is tied in with brief summers,14 and Irish summers are long, allowing leisurely growth before a very late onset of winter.15
FIG 14. Red grouse chicks, about two weeks old. (Robert Moss)
CAMOUFLAGE
Walk across a moor and you may be startled as a red grouse suddenly rises near you with whirring wings. It flies strongly with rapid beats that alternate with glides. Adept at using wind to increase speed, a red grouse moves at the same contour rather than up or down, and often swerves or tilts quickly, a habit that makes it hard to shoot.
Red grouse are well camouflaged on snow-free ground, often staying motionless when danger threatens, and are easily overlooked by man, raptor and fox. Because the birds skulk, standard methods for assessing their numbers in national surveys -such as walking across an area or standing in one spot- greatly underestimate them.
A stark exception comes on deep snow, when the contrast makes red grouse look black and strikingly conspicuous even a kilometre away. In such conditions they gather in packs up to hundreds strong, relying on safety in numbers, and on continuous snow they are so wild that they take wing when a person comes in view even 2km away. As patches of snow-free ground appear, however, they go there and become hard to see. At their tamest on sunny spring days, pairs sometimes allow one to approach to 10m.
FIG 16. Growth in grams of young Lagopus lagopus (cocks and hens combined) on Arctic Russian tundra, west Siberian forest-steppe and Irish bog.16
Notes
1. Fast growth of birds on tundra has been attributed to continuous daylight and abundant food, allowing feeding round the clock.17 However, faster growth also goes along with briefer summers,18 and tundra chicks must grow quickly in the short Arctic summer before winter’s early onset. Irish chicks on Glenamoy bog grew even more slowly in their long summers, but data are incomplete and it is not clear when their growth levels out. Such big differences among three areas are presumably genetic adaptations, although nurture can affect growth rate, e.g. wild chicks grow more slowly than well-fed captives from the same stock, on Tranøy, Norway, and in Scotland.19 The difference is, however, much smaller than the differences in the above graphs.
2. When eggs on Glenamoy bog were hatched in captivity and the chicks given a high-protein diet, their weight increased no faster. Also, wild chicks on bog where fertiliser and drains had boosted the heather’s growth and nutrient content put on weight no faster than chicks on unimproved bog. We infer that slow growth may be adapted to the long, mild Irish summer and autumn, not to the infertile bog habitat.20
3. Chicks have extremely variable growth rates. We are therefore cautious about attributing differences among studies entirely to geographical differences, especially where data are just snapshots at one age, because differences may be partly due to differences between years, or even between broods.21 Obviously this caveat applies to the above graphs.
FIG 18. Pack of grouse flying over snow. (Adam Watson)
Red grouse are wilder than other races of Lagopus lagopus, except for heavily hunted birds in Newfoundland, which formerly were tame and tended to run from a man rather than fly.22 In Alaska, willow ptarmigan are still tame away from roads,23 and white-tailed ptarmigan are also confiding if seldom molested, although shooting soon makes them wild.24
Hen willow ptarmigan seek to maximise the effectiveness of their camouflage. During spring thaws, those in white plumage tend to stand on snow, whereas hens that are partly dark stand at the snow edge, and hens in dark plumage stay away from snow.25 Similarly, when snow lies patchily on Scottish moorland, single or paired red grouse tend to rest on dark heather, where they are hard to see.26
SYSTEMATICS27
After regarding red grouse as the species Lagopus scoticus and the paler birds of Ireland and the Outer Hebrides as the subspecies Lagopus scoticus hibernicus, taxonomists later recognised both as Lagopus lagopus scoticus, one of many races of the willow ptarmigan. The paler birds also typify west Scotland and Wales, part of a gradual change from west to east in tune with the changing colour of the vegetation.
Willow ptarmigan on fairly snow-free islands off west Norway become only partly white in winter,28 and races in Kazakhstan29 and Newfoundland have some coloured feathers in their winter plumage. Another intermediate case is red grouse in northeast Scotland, for in winter they have many white feathers in this snowiest part of their range.
Captive hybrids have been bred from red grouse and Scottish ptarmigan, and from Norwegian willow and rock ptarmigan,30 and wild hybrids occur.31 In Canada, male rock ptarmigan mix with packs of willow ptarmigan before hen rock ptarmigan arrive, and a cock has been seen to sing beside a hen willow ptarmigan.32 Such events might lead to inter-specific pairings.33
WORLD DISTRIBUTION OF LAGOPUS LAGOPUS
Willow ptarmigan have the widest world distribution of any grouse, with a vast breeding range across Eurasia and America, from sea-level in the Arctic to high altitudes on southern mountains (Table 5). They inhabit Siberia’s Altay massif south to 45°40’N and Newfoundland south to 46°37’N, and they extend northwards to 76°N in Canada’s Bathurst and Melville islands, and to 76°46’N in the New Siberian Islands (Novosibirskiye Ostrova).
TABLE 5. Examples of altitudes typically frequented by breeding Lagopus lagopus. In general they tend to be at lower altitudes further north. However, at similar latitude they are at lower altitudes in regions with windier summers (Scotland versus Chilkat Pass; west and especially northwest Scotland versus northeast Scotland; Sgribhis Bheinn versus the more eastern Ben Loyal; and Kamchatka versus East Sayan. At windy Avalon they are lower than in several regions much further north).
* He gives original references for Russian sites.
In summer, they are found in the southeastern corner of Novaya Zemlya, and on the islands of Vaygach, Kolguyev and Sakhalin.34 They breed on much of the Siberian mainland, including Kamchatka, and southwards to northern Manchuria and western Mongolia, and in Sinkiang’s north corner and Tuva. During their breeding season in Kazakhstan, mean temperatures reach 23°C in July – equivalent to those found in Portugal in the same month. Birds live across most of north European Russia, and west into the Baltic States and most of Fennoscandia.
Willow ptarmigan inhabit the Aleutian Islands west to Unimak, and from Alaska across the north Canadian mainland and southern Arctic islands to the north shore of the Gulf of St Lawrence. In winter they move down to Lac Saint-Jean behind Quebec City, into southern parts of Ontario and of Canada’s prairie provinces, and occasionally as far south as northern USA states such as Minnesota.
Unlike rock ptarmigan, willow ptarmigan have not colonised Svalbard, Iceland, Greenland or the more remote Aleutians, or isolated southern massifs such as the Alps. Although they abound on the vast tundra of south and west Baffin Island, they have not been found in the more fragmented and isolated eastern valleys, despite good scrub habitat there. However, a formidable barrier of lofty mountains and ice-caps separates these valleys from the western tundra,35 thereby signifying the willow ptarmigan’s lesser mobility and flight power.
DISTRIBUTION OF RED GROUSE
Red grouse are resident on moorland over much of England, Ireland, Scotland and Wales, from the coast to the upper limit of this vegetation type. In Scotland, that limit varies from 240m on Sgribhis Bheinn in the northwest to 820m on Lochnagar in the southeast, with intermediates at 600m in the west Highlands and 760m in the Cairngorms.
Birds introduced to moorland in Belgium near the German border increased after 1920 in both countries, but after 1950 became scarce after habitat loss, and the last cock was heard in April 1974.36 Grouse were introduced to Exmoor in 1915-16, and they remain there and on Dartmoor.37 Two introductions to the Faeroes failed.38
WORLD AND NATIONAL NUMBERS
Estimates of Lagopus lagopus numbers39 vary greatly because few counts have been carried out, but they suggest a world population of 12 million in spring. Countries reported to hold most are Russia with 6.8 million, followed by Canada, the USA (Alaska) and Norway with over a million each, Sweden has 400,000 birds, the UK 250,000 and Finland 180,000. An estimate for Scotland in 2003 was 130,000 pairs on an estimated 1.2 million ha of heather moorland.40
Ireland has 1.2 million ha of bog,41 and many hills with more heather and higher grouse densities than are found on bog land. One estimate of its red grouse population was between 1,000 and 5,000 pairs.42 On this, government minister Liam Hyland commented ‘Grouse, by nature, are secretive birds, spending most of their lives hidden in heather. For this reason…their numbers here may be under-recorded.’43
HABITAT
Many publications describe and illustrate willow ptarmigan habitats abroad.44 Everywhere, birds make use of vegetation that is tall enough to conceal them from predators. Hens nest in freely drained heath45 or scrub, whereas broods frequent wet flushes or moist meadows.46
Red grouse
Most red grouse live on freely drained moorland and, less frequently, on wet heath. The former habitat resulted from deforestation by prehistoric man to create pasture or cultivated fields, since when a continuation of burning and grazing has prevented most of it from reverting to forest (see Chapter 11). Wet heath resulted mainly from a wetter climate, which led to peat growth and with it deforestation, and it too has been burned and grazed since.
Red grouse abound where their main food of short heather grows in a mixture with fairly tall heather as cover. Some of the highest densities have ‘consistently been on moors with both dry heather ground and blanket bog, where heather shares dominance with cotton-grass’.47 Cotton-grass shoots are nutritious in spring, while blanket bog supports abundant insects that are food for chicks. Even where blanket bog has eroded into peat hags, and bare peat covers much of the ground (Fig. 19), birds can be abundant.48
FIG 19. Peat hags amongst heather. (Robert Moss)
Where food abounds without cover, as on short heather after a very wide fire, only unmated cocks take territories and even they avoid the middle of the burned area. While eating short heather, birds tend to keep within a few metres of tall heather,49 to which they run if a predator approaches. However, they avoid tall dense heather, which impedes movement and offers little accessible food.
Some birds occupy open patches in woodland. Their numbers increase in the early years after planting on moorland50 if foresters have not eliminated the heath understorey, and among trees regenerating after felling or wind-throw, but they vanish before the canopy closes over.
Willow ptarmigan
After rock ptarmigan, willow ptarmigan are the most northerly grouse, breeding on flat or gently sloping land with tall heath or scrub, and in open woods of birch or conifer. In dense forest they use open patches on bogs and riverbanks, and areas cleared after lightning fires or felling until the regenerating trees close up. On mountains they inhabit a belt above forest but below the terrain used by rock ptarmigan.
In the willow ptarmigan’s range across the Canadian high Arctic, most ground is bare with very small amounts of food (Table 6), and the birds are consequently sparse. A so-called ‘polar desert’ prevails, where the summer rainfall is low, and there is little soil moisture and scanty organic matter and soil nutrients.52
FIG 20. Willow ptarmigan habitat, Dovrefjell, Norway: birch and willow scrub. (Adam Watson)
TABLE 6. (a) Standing crop and (b) annual plant production (both in kg per ha), and (c) range in spring numbers per km2 of cock Lagopus lagopus and rock ptarmigan (upper row in high Arctic and Arctic refers to Canada and lower row to Eurasia).51 Plant data were collected from Russia (Alexandrova, 1970), Scottish Alpine areas (Summers, 1978) and Kerloch (Miller & Watson, 1978); Russian plants were air-dried and Scottish samples oven-dried.
Notes for Table 6
In the Canadian high Arctic, a Salix arctica barren had an annual plant production of 3kg per ha (Bliss, 1970). Other studies showed 8kg per ha on barrens (the main habitat), 26kg per ha on a ‘cushion’ community, and 410kg per ha on snow flushes (Bliss et al., 1984). Vascular plants on Alpine tundra at Eagle Creek had a dry-matter standing crop of 2,950kg per ha and annual production of 700kg per ha (Bliss, 1970). Subarctic dwarf birch-crowberry heath on Kola Peninsula had a standing crop of 4,700kg per ha, blaeberry heath 5,300kg per ha, and heather-lichen-heath 4,900kg per ha.
# The highest densities of red grouse and Scottish ptarmigan were on fertile soils. There is also some evidence of this for Icelandic rock ptarmigan. Heidmörk, with cock densities of only 0.3-0.6, is on a lava field with sparse food plants; in contrast, Hrisey, with a density of 7-34, has continuous heath with some hay meadows (Gardarsson, 1988) that must have fertile soil, near cultivated fields with rich topsoil (Watson, unpublished).
* All plants here are combined, and comprise mostly dwarf shrubs, 750kg per ha exposed heather and 3,000kg per ha bryophyte-rich mixed heath. Lichen-rich blaeberry-crowberry vegetation produced an annual plant production of 2,ooo-2,100kg per ha.
** 1,700kg per ha of standing crop was ‘building’ heather (the growth phases are pioneer, building, mature and degenerate) and 2,700kg per ha mature heather. Both together on high moors produced 1,600-2,300kg per ha (Moss, 1969), and near the coast 3,600-4,400kg per ha (Barclay-Estrup, 1970).
^ There is less heath here than on Scottish Alpine, subarctic and low Arctic areas, as judged from studies in Japan, the Pyrenees, and the French, Swiss and Italian Alps (Soichiro et al., 1969; Boudarel, 1988; Desmet, 1988b; Bossert, 1995; Favaron et al., 2006), and from photographs in Soichiro et al., 1969, and in Bossert, 1995. Typical density. Maximum 3-4 pairs per km2 (Potapov, 1985).
FIG 21. Porcupine Creek, Alaska. Willow ptarmigan mostly inhabit the tall willow scrub and rock ptarmigan mostly the short subalpine scrub, with some overlap. (Robert Moss)
Like Britain, islands off west Norway have heather moorland where sheep grazing and burning over the centuries have destroyed trees. Here, willow ptarmigan eat mainly heather, but in recent years the moorland has been reverting to scrub and woodland as pastoral farming has declined.53 In Kazakh forest-steppe, birds rear their chicks in groves of short birch trees or scrub of birch, willow or meadowsweet, usually nesting among tall grass or meadow-sweet stems.54
DIET
Winter
At this time of year herbs die back or are covered by snow, so instead the birds must subsist on woody shrubs or trees. Willow ptarmigan take twigs or buds of willow or birch, while red grouse feed on the leafy shoots of heather or the leafless stalk tips of blaeberry. Red grouse sometimes perch on trees to eat buds and shoots, especially in deep snow, although fire and overgrazing have almost eliminated willow and birch scrub on British and Irish moors, resulting in a poorer diet for the birds.
When we see vast areas of heather shoots and flowers in summer, it is hard to imagine red grouse ever running short of food. However, sheep, cattle or red deer can greatly reduce the vegetation over winter, in the worst cases trimming it so short that it cannot offer safe cover from predators. Birds must depart or die.
Even without grazing, green heather can turn brown through desiccation within a few days if shoots lose moisture in cold weather and then cannot replace it because the soil water has frozen.55 Browning also occurs when the soil is not frozen, albeit more slowly, when dry, cold winds blow in late winter and spring -worst affected are the tender shoots of heather plants in their first year. Blaeberry and other heath species suffer less, so a moor with a virtual monoculture of heather offers much food in most years but carries with it a risk of famine.
Spring
Red grouse eat mainly heather, but in spring they supplement it with plants that begin to grow earlier, such as chickweed or sheep’s sorrel, and then blaeberry. All British grouse species eat shoots of cotton-grass where available, as these have a much higher content of the essential nutrients, protein and phosphorus than heather or other heath species. It is easy to tell when birds have eaten it from the telltale dark glumes56 in their droppings.
The hare’s-tail cotton-grass (often known locally as ‘draw-moss’ or ‘moss-crop’) abounds on thick peat. One of the earliest moorland plants to grow, it has
flower shoots that appear in late March during mild springs. By the time chicks hatch, the flower head has turned into fruits hidden in a fibrous cottony structure of beauty but bearing no nutritive value. The sparser but widespread common cotton-grass thrives in very wet patches. Its first shoots appear in May, or later on high moors and in the Alpine zone.
Cotton-grasses do not grow on freely drained moorland, so red grouse with territories in such areas must eat mostly heather in spring, which makes for a poor diet. This was the case on most parts of our study areas in Glen Esk and Kerloch.
Willow ptarmigan in Timansk (Russia), Alaska and British Columbia in spring, feed mainly on willow buds, twigs and catkins57 all nutritious and abundant. On Newfoundland’s Avalon Peninsula, where willow is scarce, almost all the spring diet comprises twigs, buds, leaves and berries of blueberry species.
Summer and autumn
Besides taking much heather and some blaeberry, red grouse in summer eat the leaves and flowers of herbs, moss capsules, flowers of bell heather or cross-leaved heath, and seeds of grass, sedge, rush and heath wood-rush. From a day old, chicks feed largely on newly growing heather shoots, which are quite tender in early summer. Moss capsules come next in favour, especially the Polytrichum species that grow profusely on wet acidic moorland. Rich in protein and phosphorus, they are almost as nutritious as insects. Invertebrates are the third commonest food, and chicks in their first two weeks eat many of them, until becoming mostly vegetarian after three weeks.58 In the first weeks they frequent flushes, where insects abound and the tall grasses, sedges, rushes and bog myrtle afford good cover. Later they use drier ground, feeding on heather, blaeberry, herbs and seeds. When poults are almost as big as their mothers in early August, some broods visit fields, eating grass seeds, clover and weeds while almost out of sight in thick cover.
In Timansk, Russia, willow ptarmigan chicks eat many insects until they are 20 days old, after which they turn to a more vegetarian diet.59 Adult birds in North America eat mainly willow and horsetail with some dwarf birch, plus various other plants, and chicks feed predominantly on moss capsules, seeds of sedge and rush, flowers and insects.60 The wet areas they frequent are presumably a rich source of insects, as in Britain.
During autumn, red grouse eat mainly heather shoots and flowers, often taking both at each peck, and smaller amounts of other items as in summer. They are fond of berries. Adult willow ptarmigan feed mostly on willow, but also take twigs of blueberry species and berries.
METABOLISM
Winter
Like poultry, grouse have a large crop that acts as a food store. By dusk it is full, bulging when seen sideways on, and holding nearly 120g.61 Its contents last through the night, so that birds are effectively fed throughout the 24 hours, and continuous digestion creates permanent heat.62 Death from food shortage during periods of snowfall seems very rare, and we have not come across it. Birds have little or no fat,63 but conserve heat by resting and roosting in snow.
In northeast Siberia, the coldest part of the northern hemisphere in winter, willow twigs contain much protein and energy early in the season. However, because birds eat the best twigs first, those remaining in late winter are less valuable. Before it is consumed, the cold food in a bird’s crop must be warmed to body temperature: twigs taken in January are at -40°C or even -50°C, and must be raised to +42°C.64 The birds are selective at breakfast, taking small nutritious twigs in leisurely fashion, whereas at the evening meal they eat hurriedly and less selectively, especially in extreme frost, when they swallow 120 twigs per minute. Over the winter they lose weight as food quality declines, until the newly growing willow shoots in spring provide a high-quality source once again.
Incubating hens
When she senses distant danger, an incubating hen becomes alert with raised head. As the threat comes near, she changes to a motionless sphinx-like posture, with head tucked in and eyes unblinking, making her easy to overlook. When a human approaches with a dog at heel, a hen willow ptarmigan that is not incubating increases her heart and breathing rates, whereas a hen in the later days of incubation cuts the rates greatly, in extreme cases down to only three to five breaths per minute (Table 7). This makes it harder for a fox to detect her, because she smells less and makes less noise or movement. On the point of fleeing, she changes from this motionless posture to rapid movement of head and eyes, and may burst out in sudden flight or distraction display.
TABLE 7. Number of heartbeats and breaths per minute in hens. First value is for Norwegian willow ptarmigan, value after comma is for Svalbard rock ptarmigan, and values in parentheses are very low rates recorded for short periods in willow ptarmigan.65
| ACTIVITY OF HEN | HEARTBEATS | BREATHS |
|---|---|---|
| Resting, including incubating | 140, 155 | 23, 25 |
| Not incubating, seeing a man with dog at heel | 255 | 31 |
| Early incubation, seeing a man with dog at heel | 140 | 13 |
| Late incubation, seeing a man with dog at heel | 100 (10-20) | 10 (3-5) |
| Leaving the nest to feed | 224, 205 | 25-28, 28 |
| On return to incubate cool eggs | 534, 442 | 35, 35 |
| With day-old chicks, approached by a man | 450-600 | 32-40 |
Notes
When a man flushed an incubating hen (willow ptarmigan and Svalbard rock ptarmigan) from her nest, the heart rate soared immediately to >500. When a fulmar flew over a Svalbard hen’s nest, her heart rate fell suddenly to 6, and an incubating Swiss hen’s steady heart rate halved suddenly when a walker came to within 10m, and then was irregular before halving again.
When a feeding hen returns to incubate eggs that have cooled to 5°C, her breathing rate increases and her heartbeat soars to over 500 per minute within 5-10 seconds of settling on the eggs, boosting the flow of blood to the brood-patch and warming her eggs quickly. It takes 40-80 minutes before these rates return to the normal resting rate of an incubating hen (a heartbeat of 140), and they rise again briefly after she turns her eggs. On rainy or cold days when her eggs cool sooner, she leaves for fewer feeding bouts, and so loses weight more quickly, which weakens her and reduces the later survival of her chicks.66
Incubating hens have very little scent. Peter Hudson reported that dogs easily find incubating hen red grouse that have many threadworms, because they smell more.67 However, incubating hens with many worms seem to survive depredation by foxes better,68 probably because they are in poorer condition and flush more readily as a fox approaches, whereas hens in good condition with few worms are more likely to take a risk by sitting tight.
Chicks
Downy chicks need frequent brooding. A day-old willow ptarmigan eventually becomes hypothermic even at an ambient temperature of 30°C.69 Hatchlings, however, respond to cold by increasing their metabolic rate,70 such that by seven to ten days they can be active for long periods at 10-15°C without daytime brooding.71 They produce heat by bursts of shivering in the breast muscles, or by walking.72 However, it is not until they are older than 14 days that these responses can prevent some hypothermia at normal summer temperatures. By about five weeks, wild chicks can survive without brooding.
When captive eight-day chicks have continuous food and heat, a drop in food quality can none the less reduce growth and survival.73 Chicks always try to fill their crops completely, and food intake is related to body-weight irrespective of their age. On cold days the small chicks cannot fully compensate for greater heat loss by eating more, and high-quality food is crucial for their growth and survival.
Captive chicks experience neither rain nor wind-chill, whereas those outdoors occasionally face a life or death struggle with the elements. Heavy rain or snow can kill chicks that are even two to three weeks old.74 Kjell Erikstad found that cold and rain shorten the time that chicks spend feeding away from their mother’s warmth, and also reduce the availability of the insects they need for growth and survival.
MOVEMENTS
Long-distance seasonal movements or migration
Some spectacular movements of Lagopus lagopus have been seen, such as 10,000 willow ptarmigan flying north through a pass in Alaska’s Brooks Range one early morning in April.75 The following explanation probably applies also to rock ptarmigan, because salient features in both species are similar, but more is known about Lagopus lagopus.
Northern regions have snow every winter, but much of the food in forest and scrub remains uncovered, so birds there are resident. Snow usually covers the shorter vegetation on hills or tundra, and here most birds move away, either flying uphill to ridges where drifting uncovers plants, or to valleys with scrub or trees.76 How far they move depends on how far the nearest suitable wintering grounds are from the summer range. In British Columbia’s Chilkat Pass and in most parts of Alaska, birds travel 20-50km, whereas many from tundra regions north of the Brooks Range fly south for 160km to woodland, and birds in Manitoba have been seen 8ookm south of the breeding range. From islands and mainland tundra in Arctic Russia, birds move up to 250km south and many cross 75km of sea, although some stay on the tundra if snow has not covered all plants.77
Birds in the Brooks Range move from late September, with a peak number departing in mid-October; at Chilkat Pass all have departed by mid-December; and in Russia they move between October and January. In all regions, cocks move later in autumn and for a shorter distance, and hens leave earlier and travel further. During spring, conversely, cocks head for the summer grounds earlier than hens, and arrive there sooner. In short, large-scale annual movement in far northern regions is frequent enough to be called migration, but its timing is irregular, depending on snowfall.
Movements are more noticeable when more birds participate, either because population density is high or because snow covers most food. When irregular, such movements are often referred to as irruptions. When more birds move away from areas with higher densities, this is known as density-dependent movement.78 Whether high density can induce mass movement has not been studied in willow ptarmigan, but this seems likely from observations of rock ptarmigan in Greenland (see Chapter 4).
A recurring feature in writings on red grouse is ‘grouse migration’. This involves the sudden appearance or disappearance of many birds, sometimes in snow-free periods and hence ruling out movement caused by sparse food. An example of such an appearance occurred at Glen Esk in 1959, when numbers almost doubled on the high study area in October and stayed dense until January.79 An example of a disappearance involved many pairs leaving their territories in springs of high population density at Kerloch during the 1970s.80 The evidence suggests that ‘grouse migration’ comprises irruptive movements that occur at high or declining densities during population fluctuations.81
Short movements to food
Red grouse easily scratch through shallow snow to uncover plants, but feeding becomes unprofitable when deep snow covers most vegetation. If snow blankets
low moorland, birds often fly uphill to ridges where winds have blown it off the heather, but if yet lower moorland nearby has less or no snow they will fly there. Occasionally, packs of birds have been seen flying towards land with less snow, and many such records have been collated.82 During the snowy winter of 1950/1, grouse deserted the upper glens of the Cairngorms for several months, gathering some 10km away on lower glens and near open woodland where less snow lay.83 Movements in snow can occur between late October and April, but in most winters the snow is incomplete and birds remain in residence.
In late summer and autumn, willow ptarmigan often move to high ground where late-growing plants offer a nutritious bite.84 In Scotland, many red grouse fly from high moorland to Alpine land in July-August, occasionally being seen at altitudes of up to 1,010m in September85 and, infrequently, even at 1,040m in September-November on ground devoid of heather. Birds on lower moorland usually stay there, but sometimes they move up to 2km to abundant berries. Red grouse, blackgame and capercaillie formerly ate oats in fields and stack-yards, flying 1-2km to do so, but this stopped after farmers began using combine harvesters.
Natal dispersal, philopatry, emigration and immigration
Natal dispersal is the movement of young birds from where they hatch to where they first breed. In all British grouse species it begins each autumn, when broods break up and youngsters separate from their mothers and from one another, and it gives youngsters a chance to move to less crowded land. Hens move further than cocks,86 thereby reducing the adverse effects of inbreeding. Not all youngsters disperse far, and some – especially cocks – breed near where they hatched. This tendency, which is the opposite of natal dispersal, is known as philopatry.
Breeding dispersal is the movement of old birds between the places where they breed in one year and the next. In red grouse and Scottish ptarmigan, old birds tend to return in a later year to the same ground where they bred previously.87 Being familiar with their old domains may help them breed successfully.
Natal dispersal
In a study where gamekeepers on many moors ringed young red grouse, 739 were shot in their first shooting season, within a few weeks of being ringed.88 Although grouse can be driven up to 5km for shooting,89 only two birds had gone beyond that distance, during a period when most young are still with their parents. Of the 290 recovered in later seasons, however, 9 per cent had moved beyond 5km, one of them from Deeside to Drumochter, 42km west as the crow flies. In short, most movement occurred after the youngsters’ first shooting season.
In most grouse species, two main periods of natal dispersal have been reported, in autumn and spring (see Chapter 14). Young red grouse and Scottish ptarmigan, however, have already taken territories by spring. Despite this, some desert their territories and move just before nesting, probably to breed elsewhere.90 This movement is density dependent, occurring most commonly in years of high population density. In red grouse at Kerloch, it occurred mostly at densities above approximately a pair per hectare.91 Such movement may include old red grouse (breeding dispersal), but evidence is very scanty.92
Philopatry in red grouse
At Kerloch, where we marked hundreds of territorial birds and chicks, many young cocks in their first autumn took territories on or beside the territory of their father, uncle or brother, while most young hens settled further away. Related young and old territorial cock neighbours were less aggressive to one another than to strangers. As a result, clusters of closely related cocks formed, most noticeably during the years of a cyclic population increase. In years of peak and decline, young cocks tended to take territories further from their fathers, as aggression increased and numbers fell.93 Studies since then, at Glas-choille and elsewhere, have increased understanding of philopatry, aided by new techniques of measuring relatedness that use DNA from feathers (see Chapter 14).
Emigration and immigration
Natal dispersal and philopatry involve individuals, but their movements have consequences for whole populations, namely losses from emigration and gains from immigration. At Kerloch, summer emigration of red grouse with chicks was more frequent than spring emigration, and occurred especially during a big cyclic decline in numbers. Families usually left the study area once the chicks could fly well at three to four weeks, but in the mid-1970s, years of a very steep cyclic decline, pairs walked away southwards with day-old chicks. Adults returned in autumn without young, presumably having reared them elsewhere. A case of immigration occurred at Kerloch in the summer of 1971, years before the above decline, onto an area where we had boosted the amount and nutritive value of heather by applying fertiliser. Birds with chicks arrived from elsewhere and then stayed until their young were fully grown.94
To conclude, autumn dispersal of young is a normal event, but other movements also occur, notably at high densities and during cyclic declines in numbers.
AVERAGE POPULATION DENSITIES
Red grouse
Just as heather becomes scarcer in areas of wetter climate in Britain or Ireland, so too do red grouse.95 In eastern Scotland and northern England, average densities in spring are tenfold or more higher than those in west Scotland and Ireland.
Muirburn, or the controlled burning of heathland and moorland, is commonly practised in Britain and Ireland with the aim of increasing grouse densities, and it works. That narrow fires lead to a rise in average grouse density has long been known.96 Average densities and bags are related to the extent of heather, to the percentage of young heather after muirburn, and to the pattern of muirburn (higher densities follow narrow fires). In an experiment at Kerloch, a patchwork of narrow burnt strips increased the number of territorial grouse almost twofold three years later,97 and similar treatment on a heather-dominated hill at Glenamoy boosted grouse numbers threefold.98 When we repeated this on the Isle of Mull, the number of territorial cocks rose threefold on ground open to many sheep, and sevenfold where a fence excluded sheep.99
Average grouse density is also affected by bedrock, through its influence on soil fertility, provided that the rock is not overlain by thick peat or glacial deposits derived from different rock. An early finding in northeast Scotland, where most study areas were freely drained and had little or no thick peat, was that average densities over base-rich rock exceeded those over acidic granite.100 Heather over base-rich rock had a higher content of the vital elements nitrogen and phosphorus than that over granite, and David Welch found more herb species, some of them indicators of fertile soil.
FIG 24. Moorland on Strathdon with heather-burning patchwork, conifer plantations, three self-sown Scots pines and arable fields. (Robert Moss)
In a later study where bedrock was graded on many English and Scottish moors, it made only a minor contribution to explaining average bags.101 Thick peat covered large extents of the studied moors, however, thus negating a strong influence from bedrock. Another confusing factor is that cotton-grass shoots boost the birds’ nutrition in spring, irrespective of bedrock. On freely drained moors in east Scotland and England, this rich food source does not occur on most territories, but it does abound on thick peat.
Average bag sizes in England and Scotland
English bags of red grouse tend to be bigger than Scottish ones, and counts confirm this. ‘English moors tend to support more grouse per unit area than Scottish ones; limestone and other base-rich rocks occur widely and support more nutrient-rich food-plants…Many produce large bags of grouse from a sward management regime that would yield few grouse from the average Scottish moor over poorer rocks.’102
Other reasons also help to explain the superior English performance. Archaeologists know of widespread prehistoric cultivation of moorland,103 and early agriculture boosted soil fertility for centuries, perhaps irreversibly (see Chapter 11).104 Most English moorland has gentle slopes that are conducive to cultivation, which in the Middle Ages took place in the Pennines, Yorkshire Dales, North York Moors, Dartmoor, Exmoor and north Wales.105 This would have improved soils beyond the capability of those derived naturally from the often poor local bedrock. Subsequently, peat would have swamped much of the improved soils on rainy western moorland, as in Mayo and Jura (see Chapter 11), but on less rainy eastern moors most ground remained freely drained, and improved soil fertility due to cultivation would have continued.
In addition, because summer temperatures decline northwards, most English moors are warmer than those in northeast Scotland, for example 1-2°C warmer in July. These warmer temperatures allowed cultivation of English moorland to higher altitudes than in more northerly areas, again contributing to the current greater fertility of much English moorland.
Although base-rich rocks underlie most English moorland, a large area lies above hard acidic millstone grit, which weathers into poor soils and yet supports some of the most productive grouse-moors. This may be because cotton-grass abounds on the peat that blankets much of this moorland, affording good food for grouse in spring. Also, precipitation and fog have transported pollutants from urban factories located near the north England moors, depositing compounds of nitrogen and phosphorus there.106 This fertilising of heather could well have maintained abundant grouse even over poor bedrock.
Following on from this, we wonder whether recent grouse declines may be partly attributed to a reduction in old-style heavy industry. Nitrogenous compounds created through the combustion of fossil fuels and intensive production of livestock are still deposited on moorland, but the deposition of phosphorus compounds has fallen in conjunction with the decline in heavy industry. This may partly explain the smaller grouse bags shot in recent decades on some north England moors.107
A survey of red grouse on many English and Scottish moors revealed that the average bag increased with June air temperature and with estimates of heather production, and to a lesser extent with the presence of small burnt patches, a varied age of heather and the base richness of bedrock.108 English moors have warmer summers than Scottish moors at the same altitude, and summers with warm Junes boost heather production. Hence one would expect big bags more often on English moors for this reason.
The same survey showed that there is a higher density of keepers (more per unit area) in England than in Scotland, and that a high density of keepers went along with bigger bags. Presumably this was due to the beneficial effects of keepers, rather than that more keepers were employed on areas that support bigger bags for other reasons.
Willow ptarmigan
In the high Arctic, each estimate of density (see Table 6) covers only one or a few years, but estimates from different years, areas and observers are all low, so it is reasonable to conclude that average densities must be low. Densities in high-Arctic and Arctic Canada are particularly low, and are exceeded by densities in the same zones in Eurasia. This goes for rock ptarmigan in these two zones also, so we include data on them in the table for comparison.
Densities of willow ptarmigan are higher on Arctic tundra and subarctic terrain than in the high Arctic, but low in boreal woods and very low in Kazakhstan forest-steppe. Typical densities of 5-10 pairs per km2 occur in Sweden and Norway.109 Densities are low in the Swedish Highlands,110 and most birds in southern Finland and the Baltic states live on forest bogs at densities lower than on treeless tundra. Densities on tundra and forest cannot be compared directly, however, because essentially the entire tundra is available as a habitat for the birds, but in forest only the edges of bogs or water bodies are occupied. Measurements of territory size would overcome this snag, but these data are not available in forest.
There is a low average density on the Avalon Peninsula in Newfoundland, and successively higher densities at Canada’s Anderson River and Norway’s Dovrefjell.111 At British Columbia’s Chilkat Pass, minimum and maximum figures indicate that the average density must be yet greater.
Burning of subalpine heath to increase willow ptarmigan densities, in emulation of muirburn for red grouse (see p.46), has been carried out at altitudes above 1,000m in south Norway. After fires were burned on 15 per cent of land in two areas, counts of territorial cock willow ptarmigan rose higher than on untouched areas, and remained so for a decade.112 However, it was noted that little recovery of vegetation occurred after burning of lichen-dominated ground, and ‘fires may cause semi-permanent damage if set in sensitive areas’. Burning cannot be recommended on subalpine heath, because of the risks of destroying the thin topsoil and seriously delaying vegetation recovery.
On offshore islands
Willow ptarmigan occur at higher densities on the small islands of Tranøy, Norway, and Brunette, Newfoundland, than on the nearby mainland, and on the Icelandic island of Hrisey the same has been found to be true for rock ptarmigan.113 Because there are no foxes on Brunette or Tranøy, no stoats on Tranøy in most years, and on Hrisey no mammalian predators and very little egg-robbing by crows or ravens, the high bird densities might be attributed to the unusually few predators.
Other issues confuse the story, however. Cattle and then sheep damaged Tranøy’s vegetation, and five successive years of the highest grouse densities followed the end of dairy farming as the vegetation recovered. More scrub grew on Brunette Island than on the mainland, where much of it had been destroyed by fires. Hrisey’s vegetation was changing rapidly during the study, growing taller after sheep stocks had fallen, and to us the heath seemed less grazed than on the mainland. Hence in each case the predators and habitat were confounded. It seems likely that habitat quality on the islands exceeded that on nearby mainland, though deteriorating on Tranøy latterly. Also, owing to an island’s relative isolation, movement between it and the mainland may be more constrained, which might increase island densities.114
The islands in these studies illustrate another snag, namely that biologists often choose areas with high population densities because this gives large samples for analysis. If islands are unusual, their results cannot be applied to the mainland, especially if the nearby mainland has no study area (as with Tranøy and Hrisey). We conclude that there might be an ‘island effect’ that causes high population densities, but if so the reasons are not clear.
The effect of food abundance and habitat fragmentation
We attribute the very low densities of high-Arctic willow and rock ptarmigan to the scarcity of food plants and their low annual production (see Table 6), combined with a lack of tall vegetation as cover. Greater densities of birds in Eurasia compared with the equivalent zone in Canada fit this explanation. Likewise, higher population densities in the subarctic and yet higher densities on British moorland go hand in hand with a greater abundance of food plants. Vegetation on a very few areas has the opposite effect, as it grows too tall and dense for easy feeding, which thus accounts for low bird densities in forest. In Kazakhstan, we think that a lack of bogs and scarce food plants for chicks in the forest-steppe here are additional reasons for low densities.
Some particularly high densities of red grouse have been recorded (Table 8). At Kerloch, where an application of ammonium nitrate fertiliser increased the heather’s growth and nutrient content, birds reached the highest density of pairs so far recorded. Apart from this artificial case, the greatest known density of pairs was on uppermost moorland at the Cairnwell. Because of the windy subalpine climate there, vegetation stays more or less unchanged without burning, forming a fine-grained patchwork of short heath for feeding and slightly taller heath for cover. Also, the soils are relatively fertile and so heath plants are nutritious.
Notes
Brown & Watson (1964) gave other low densities of adults and full-grown young (e.g. on moorland valleys), including 2.3 near Tyndrum in Argyll and 1.3 in northwest Sutherland.
# Areas with fertiliser applied to heather.
FIG 25. Short, windswept heather on unburnt subalpine moorland at the Cairnwell, by the ski area car park. A few sheep grazed the area in late summer but had little effect on heather height. The dogs are pointing at a brood during a count of adults and chicks, used for measuring breeding success. (Adam Watson)
Fragmented habitat supports low average densities of red grouse. The same is true of American ruffed grouse, whose habitat was broken up by farmers into isolated or poorly connected patches.122 Red grouse on isolated patches or promontories occur at lower density than those in the midst of uninterrupted moorland (see Chapter 9).
Year-to-year fluctuations in density
On any one area, the number of birds changes from year to year. These fluctuations can be studied from bags or counts. Bag records often cover many years, but they exaggerate the size of fluctuations and usually confuse adult density with breeding success. Bags fluctuate on some areas in fairly regular cycles, whereas on others they do not. In a study of bags on 289 moors, 63 per cent showed evidence of cycles, with an average period of about eight years.123 The period rose from south to north, from about seven to about nine years.
It should not, however, be concluded from this that cycles or cycle periods are fixed characteristics of a given part of the country. On Deeside in Aberdeenshire, studies on individual estates reveal a more varied picture. Counts show a ten-year cycle on acidic upper moorland in the Cairngorms,124 but erratic fluctuations on base-rich upper moorland at the Cairnwell. Further east there has been an eight-year cycle in bags at Invercauld,125 no cycle in bags at Glen Tanar, and a seven- to eight-year cycle in counts and bags at Kerloch.126 Bags can show different periods even on one moor, as at Rickarton, with a six-year period in the late 1800s and a ten-year one after 1945.127
In addition, long-term records sometimes show runs of clear cycles, interspersed with less regular fluctuations. Sometimes, cycles on an area stop altogether. The Finnish six-year cycle of hazel and black grouse and capercaillie in 1964-83 was so regular that a paper describing it carried the title ‘The clockwork of Finnish tetraonid population dynamics’,128 yet it ceased soon after publication. Cycles also occasionally change in period length. During the first half of the 1900s, Finnish tetraonids (including willow ptarmigan) showed three-to four-year fluctuations, much shorter than the later six-year ‘clockwork’.129
Willow ptarmigan show three- to four-year cycles in Norway and Sweden, best recorded by Svein Myrberget on Tranøy.130 These are often associated with three-to four-year cycles of voles and lemmings.131 In the alternative prey hypothesis (see Chapter 14), predators switch to eggs and chicks when their main rodent prey becomes scarce, so willow ptarmigan rear fewer young and a decline in their overall spring numbers follows.
Tranøy, however, supported no predators that specialised on rodents, save for stoats, which did take many eggs of willow ptarmigan in a few years, though they were absent in most. One out of six measured troughs in breeding success occurred a year before rodents crashed, which is not what would be expected from the alternative prey hypothesis. Also, two declines followed summers with low egg losses and an absence of stoats. At Lövhögen, Sweden, only three out of five measured troughs in breeding success coincided with rodent crashes, and one rodent crash coincided with a peak in the birds’ breeding success. Hence losses as a result of prey switching were not necessary for poor breeding or subsequent declines.
Furthermore, winter loss of young was found to be the most important factor determining year-to-year change in spring numbers.132 This was also the case in six other studies of Lagopus lagopus and rock ptarmigan that provide enough information to reach such conclusions. A lower percentage of young recruited to the breeding population was a main determinant of population decline.133
A wider geographical perspective is instructive here. Finnish voles and lemmings also show cycles at about three to four years, while Finnish hazel and black grouse and capercaillie do not, so the idea of prey switching falls down here. Willow ptarmigan on Newfoundland’s Avalon Peninsula, at the Anderson River in Northwest Territories and at Chilkat Pass in British Columbia have fluctuations of 8-11 years, and at Kolyma in Siberia the population peaks about once per decade,134 even though voles occur at all four areas and lemmings are also found at Anderson River and Kolyma. The three- to four-year cycles of Norwegian birds therefore seem unusual.
To conclude, a switch in prey by predators from rodents to eggs and chicks may be sufficient to cause some cyclic declines in Scandinavian willow ptarmigan, but not all. It may perhaps be sufficient to ‘entrain’ the fluctuations (influence their timing, as distinct from actually causing declines – see Chapter 14), but this has apparently not been studied. Switching cannot explain cycle periods other than those lasting three to four years.
The amplitude of a population fluctuation can be calculated by dividing the highest density by the lowest. Amplitudes from autumn counts (which include young) usually exceed those from spring counts. Big spring amplitudes for a single fluctuation were about 14-fold on Brunette Island for willow ptarmigan and at Forvie for red grouse. However, amplitudes of less than twofold occur, e.g. only 1.6 at Corndavon, and we regarded a fivefold fluctuation at Kerloch as large.135
Even within one moor, the timing of fluctuations can vary on different parts. On Kerloch, changes in the density of red grouse between 1962 and 1978 began on high ground next to continuous moorland and furthest from farmland and woodland, and then spread downhill until the lowest ground showed a similar decline.136 This ‘travelling wave’ moved downhill at 2-3km per year, and we presume that it involved a change in grouse behaviour in response to high density. This is the only documented case of a travelling wave in British grouse species, but similar waves have been found in field voles at Kielder and in Canadian snowshoe hares. Probably they are often overlooked.
Long-term declines
British bags of red grouse show a long-term decline in most regions,137 and Irish bags show an even bigger decline.138 Bags in the Outer Hebrides dropped after 1916, and fell to almost to zero after 1940.139 In western Ireland, relatively big bags before 1914 fell after 1918, shooters bagged few birds in the early 1930s, and sport shooting almost collapsed after 1945.140 Long-term declines further east in Scotland and England began later, with a big fall in the 1940s.141 The changes from west to east bring to mind the possibility of a large-scale travelling wave in grouse density.
Very deep declines of red grouse in Britain and Ireland in the 1940s occurred also in Scottish bags of ptarmigan, blackgame and capercaillie.142 Ptarmigan numbers in the Cairngorms dropped very low in the mid-1940s, as did numbers of red grouse on high moorland there.143 Finnish bags of willow ptarmigan, blackgame and capercaillie also fell to unusually deep troughs in the 1940s, and in northern European Russia there were widespread declines in these species and in rock ptarmigan around 1939, and very low troughs in the early 1940s.144 Therefore, management peculiar to Britain or Ireland cannot explain the size of declines or the depth of troughs over such a huge area, and a wider factor such as climate must have been involved.
In the decade after 1945, bags of red grouse did recover on some British moors, and numbers of red grouse and ptarmigan rose in the Cairngorms. Bags of Finnish blackgame and capercaillie recovered partly, though not until the 1960s, and then declined after the 1970s. This pattern resembled the particularly high numbers of red grouse and ptarmigan in northeast Scotland around 1970 followed by big declines in the mid- and late 1970s. However, bags of red grouse in many parts of Ireland and Britain failed to recover to former heights, despite partial recovery in the 1960s and 1970s. Hence big declines and deep lows were general occurrences but recoveries were not.
Failures to recover might be attributed to habitat becoming less suitable or fragmented, or to more predators, but this is not the whole story. Any attempt to explain population declines in the 1970s by confining attention to local management in Britain or Ireland would be insufficient. To illustrate a wider approach, consider bags of red grouse in northwest Scotland and willow ptarmigan in southeast Norway (Fig. 26). In 1900-85, bags of each rose and fell remarkably closely, both declining from an initial high density.145 Scottish and Norwegian birds are subject to different climate, food, habitat, disease, parasites, predators and management. Hence the similar long-term downward trend may involve a global factor such as climatic change or pollution, affecting both countries. Therefore, wider changes can override local ones such as keeper numbers or other land management factors. It does not follow that management is unimportant – far from it – but wider issues provide us with a better understanding.
On some moors that formerly provided big bags, fewer keepers have undoubtedly resulted in poorer muirburn, less killing of foxes and crows, insufficient control of browsing, fewer grouse and smaller bags.146 Even where keeper numbers and standards of management have not fallen, however, bags have fallen on many moors. Pessimistic attitudes and insufficient shooting effort are often to blame (see Chapter 15).
In contrast to the overall pattern, long-term declines did not occur on a few Scottish and English moors. If widespread climatic change caused general decline, as suggested above, management of such moors must have improved. This involves good muirburn, effective control of grazing and of foxes and crows, and reliable counts of grouse, along with rational policies for shooting. On a few moors where there had been long-term declines, such new management led to increased bags in the late 1980s and early 1990s.147
FIG 26. Bags of willow ptarmigan shot in southeast Norway and of red grouse in northwest Scotland in 1900-85. The data points are five-year centred averages, from ‘Rypa’ estate in Norway (61.5°N, 10.5°E) from Hjeljord & Kiær (1991), and means from areas 1, 2 and 3 from Hudson (1992).
SURVIVAL
Most estimates of annual survival rates in Lagopus lagopus rely on finding which adults that have been marked on a study area return to it the following year. Because this assumes that adults do not move to settle outside the area under study, such estimates of survival are minima, more properly termed ‘return rates’. Adult survival rates and return rates are the same if breeding dispersal is negligible, but differ if it is not.148 Survival can also be calculated from counts of unmarked birds, but these estimates can be biased if the overwinter survival of yearlings differs from that of old birds.149 Survival often varies widely on a given area from year to year; Table 9 gives averaged values.
TABLE 9. Mean annual return-rate of marked adult Lagopus lagopus.
Adult willow ptarmigan in North America and Scandinavia seem to survive better than red grouse. It follows that, given similar breeding success, willow ptarmigan in their first winter must survive worse than red grouse in theirs. Perhaps experience confers more advantage in the land of willow ptarmigan than on British grouse-moors.
Cock Lagopus lagopus generally survive better than hens. This tallies with many counts showing more cocks than hens in spring, and with the generalisation that cocks survive better than hens in most grouse species.151 Measured survival does not decline with age. Also, the average survival of red grouse – adult cocks and hens combined – appears to be the same (33-35 per cent), irrespective of shooting.
Because survival in Lagopus lagopus does not appear to decline with age, it does not follow that birds are potentially immortal. Rather, most birds die before they reach their physiological age limit. An indication of this limit is given by the longest-lived individuals. A hen red grouse that had been tagged as an adult on an English moor in spring 1980 produced a brood in each of the next five summers until she was shot in November 1984 when at least five years old.152 A red grouse was recorded alive in its eighth year in a national ringing scheme, and two cocks at Kerloch lived into their seventh year and a third cock into his eighth.153 At Glas-choille, an eight-year-old cock that had hatched in 1994 was still territorial in spring 2003. A willow ptarmigan in its ninth year occurred in Norway, and a nine-year-old cock willow ptarmigan and an eight-year-old hen were recorded at Chilkat Pass, British Columbia.154
NUMBER OF HENS PAIRED WITH COCKS
Most territorial cock Lagopus lagopus pair with a hen each, a few have two hens, and a few remain unmated. In Canada and Scandinavia, where abundant willow offers nutritious food, most cocks are mated. On British and Irish moors, however, where burning and overgrazing destroy almost all willow, many unmated cocks occur, especially over poor soils. Spring counts of willow ptarmigan on British Columbia’s Chilkat Pass, Newfoundland’s Avalon Peninsula and the Norwegian island of Tranøy show only a small excess of cocks, far less than in most years on infertile Scottish moors.155 In years of peak density and decline on infertile soils over granite in Scotland, up to half the territorial cock red grouse are unmated, and occasionally more.156 On fertile moorland soils, however, or where cotton-grass affords a rich spring diet, we see a higher percentage of mated cocks.
A big excess of territorial hen red grouse has been found only in experiments. One case followed the removal of all territorial cocks in autumn,157 and another a boost by fertiliser to the heather’s production and nutrient content. When Susan Hannon removed territorial cock willow ptarmigan in spring at Chilkat Pass, she also found more hens than cocks subsequently.158
We conclude that the sex ratio of territorial red grouse in spring is usually fairly even, but that a large male excess tends to occur on poor soils, especially in years when densities are high or declining. A hen excess can occur after cocks are removed, and after fertiliser has boosted nutrition.
DATE OF EGG-LAYING
Lengthening days stimulate gonad development, but the day length required for hens to lay varies with local climate.159 Willow ptarmigan at 690N in Arctic Canada or Arctic mainland European Russia lay their first eggs in early June, under continuous daylight. On the colder, snowier Kolguyev Island, also at 690N, they do not lay until late June, and in the even snowier Canadian high Arctic they do not lay until the end of June or even into July. Hens at 690N in north Norway lay three to four weeks earlier than hens at the same latitude in far snowier Arctic Canada.
At 57°N, red grouse on coastal moors near Aberdeen begin laying in early or mid-April, three weeks before hens at 70°N in north Norway. In Glen Esk, inland from Aberdeen at an altitude of 200-300m, they lay at the end of April, while on nearby hills 300m higher they lay a week later.
When captive Scottish hens from 57°N and Norwegian hens from 70°N were given artificially longer days by electric light, Scottish hens laid their first eggs when the photoperiod reached 15 hours, Norwegian hens did not lay until it reached 19 hours, and hybrids were intermediate at 17 hours.160 Hence inherent factors determined their responses. In conclusion, different populations use increasing day length in such a way that their response fits the average local climate.
On any one area, hens lay earlier in mild springs than in cold ones, in tune with the earlier growth of food plants.161 Some individuals also lay earlier than others nearby, e.g. heavy hens lay early on the Norwegian island of Tranøy and at Chilkat Pass, British Columbia.162 In red grouse at Kerloch, the spread was approximately three weeks in any one year, and about 80 per cent of clutches hatched within two weeks around the median date.163 Individual hens that were early in one year tended to be early in the next, suggesting that some are inherently early.
NESTS AND INCUBATION
Hens nest in their first summer and normally every hen nests.164 A hen that seems not to be nesting may have deserted her nest or lost it to a predator. We know of only two individuals that we think did not nest, both of which were in poor condition and carrying many worms.165
The hen chooses the nest site, which in red grouse is usually in vegetation that is taller than average for the area and typically beside an open patch where she can easily escape.166 Some choose differently, such as willow ptarmigan beside driftwood logs on Pacific beaches adjacent to forest.167 One hen at Kerloch made
an extraordinary, easily seen nest on a deep, wide patch of oat straw that had been left as cattle food.168 At Kerloch and Spyhill, where few foxes occurred during our studies, several hens nested on recently burnt patches or in tufts of partly burnt heather, but we saw no such open and easily seen nest at the fox-ridden Rickarton.
When leaving the nest after laying, a hen usually covers her eggs with plant litter, which hides them and reduces their cooling in frost, although incubating hens generally leave eggs uncovered when leaving.169 Eggs can fail to hatch if they freeze before incubation starts,170 but frosts down to -3.50C did not prevent subsequent hatching in Arctic Russia.171 Incubated eggs do not freeze when hens leave to feed, because warm eggs in an insulated, sheltered nest cool slowly.
During snowfalls before incubation, occasionally a Scottish hen cannot find her nest and lays an egg on the snow,172 and later it can be seen lying on the ground. Heavy snowfalls during incubation can have worse effects, forcing some Swedish and Scottish hens to desert their nests.173
Hens incubate their eggs for about three weeks.174 In northern Russia, Finland and Norway, they spend about 95 per cent of the 24 hours of each day incubating, with three to four trips per day off the nest, averaging about 20 minutes each. In comparison, red grouse at Kerloch were off the nest two to three times per day.175 Disturbed hens that leave the nest quickly may knock a few eggs out for a distance of 10-20cm, but will retrieve them on return. Even when Russian ornithologists rolled four to seven eggs for 5-20cm out and lightly covered them with grass, all eggs were back in the nest later.176 After a hen has left her nest, she voids a ‘clocker’ (broody) dropping about 30-50cm long and 30cm across, usually some distance away. As in incubating fowls, clocker droppings are the result of storing faeces in the large intestine. Hen grouse do not void in their nests, except during prolonged hatching or in very bad weather when they delay departure with their chicks.
In an average 7 per cent of nests at Glen Esk, eggs were lost to predators, this figure rising to 11 per cent at Kerloch, and to 31 per cent at Glenamoy.177 More crows and foxes occurred at Kerloch than at Glen Esk, and yet more at Glenamoy. In two Norwegian studies, 15 and 17 per cent of nests failed because of egg predators, and in the first study predators also took 5 per cent of incubating hens.178
CLUTCH SIZE
Like poultry, captive Lagopus lagopus continue to lay many eggs beyond the normal clutch size if they are removed daily. It has been suggested that hen bantams observe the clutch and thereby determine the number of eggs still to be laid, and that this might also apply to wild grouse.179 However, when we removed some eggs from nests of wild red grouse, the hens did not lay extra eggs beyond the typical clutch size, even though they saw a smaller number of eggs than usual.180 They finally incubated two to four eggs when the mean clutch-size was seven to eight, and willow ptarmigan act similarly.181
Clutch size shows no clear relation with latitude in North America182 or Eurasia (Table 10). Within Britain, the mean in different studies varies from 7.4 eggs at Glen Esk to 9.4 on Strathmore. We think that this is related to the nutrition of laying hens, clutches being bigger on peatland where many cotton-grass shoots are available or where freely drained fertile soils support nutritious food plants. Strathmore consists chiefly of blanket bog with much cotton-grass, and lies on millstone grit with some outcrops of limestone. Cotton-grass was uncommon at Glen Esk, and abundant sheep, along with mountain hares and red deer, ate most of the first shoots.183
The average clutch size of Lagopus lagopus differs from year to year on a given area, and is bigger in years when hens lay early.184 Also, heavy hens lay larger clutches.185 The link is that early plant growth offers prime feeding, whereas later growth becomes fibrous, with less protein, phosphorus and energy. Thus, the early melting of snow and consequent good nutrition influence the weight and clutch size of hens in Arctic Russia.186 The effect of spring food on clutch size works via the condition of laying hens. For example,
hens at Glen Esk laid on average 6.1 eggs in 1959, a year when 14 per cent of adults died in poor condition and contained many threadworms, after heather suffered severe browning. The average clutch size rose to 8.1 in 1960, when only 2 per cent of adults died in poor condition and contained few worms, after hardly any browning.
Individual hen red grouse that lay early on a given area and within a given year tend to lay bigger clutches than late layers.187 On the Norwegian island of Tranøy, early laying willow ptarmigan tended to outweigh late-laying ones.188 Also, hens weighing less than 475g laid on average 7.5 eggs, compared with 10.7 eggs by hens weighing over 625g.189
A hen that loses her first clutch often lays a repeat, this having three to four fewer eggs. Hens that have lost chicks do not usually re-lay, but there is fairly good evidence of a hen red grouse re-laying after losing her first brood when the chicks were about a week old.190 Occasionally, hen red grouse and willow ptarmigan renest twice or, rarely, thrice.191 Renesting results in a late brood, which in Scotland is often a month behind. Aged only six to seven weeks at the start of the shooting season on 12 August, these grouse ‘cheepers’ call loudly when flushed, and they seldom reach the butts in a drive. On the Norwegian island of Karlsø, where willow ptarmigan lost 27 per cent of their first clutches, renesting compensated in the short run for 45 per cent of lost eggs, and chicks survived up to four weeks as well from renesting as from first nests.192 In Canada, however, a smaller percentage of birds raised from renesting returned in the following year. Also, youngsters from renest broods cope less well with the coarse winter diet.193
BREEDING SUCCESS
Breeding success is the number of chicks reared per adult or per hen, including hens with no chicks. It comprises the number of young reared per successful hen (called brood size), multiplied by the proportion of hens that rear chicks. At Glen Esk, for instance, 83-95 per cent of hens raised young in three years of good breeding, but almost half failed in two years of poor breeding.194
Table 11 shows some examples of breeding success. Clutch size, hatching success and nest loss all affect breeding success, with nest robbing by predators particularly severe in some years.195 In studies of red grouse and Scottish ptarmigan, however, chick loss had far more influence in most years, occurring mainly in the first few days after hatching. The viability of hatchlings determines their survival in the first week – even in captivity, where they have continuous food, water, heat and shelter. Their viability depends on egg quality, which in turn depends on the hen’s condition and diet. In Sweden, Rolf Brittas found that mild springs led to early plant growth with nutritious food, which boosted the fat reserves of hen willow ptarmigan and led to good survival of chicks.196
TABLE 11. Number of young Lagopus lagopus reared per adult, and mean number of young reared per brood, approximately in order from north to south.
Notes
Some data are not strictly comparable because in a few cases counts were carried out long before young were reared – as early as two to four weeks on Norwegian areas, the Anderson River and the Chilkat Pass. Only on British and Irish areas were young counted when fully grown.
# Mean of all broods in three years, not mean of annual means as in other rows.
The quality of food for laying hens on British and Irish moorland has declined in the last few centuries, because sheep, cattle and red deer, along with muirburn, have almost eliminated willow and birch scrub, and the animals also feed heavily on other nutritious food such as cotton-grass shoots. For example, grouse breed poorly at Glenamoy, where heather on thick peat has a low content of phosphorus. In spring, freshly growing cotton-grass shoots abound and grouse eat them avidly, but intense competition from sheep and cattle leaves them very little.197 If moorland is not overgrazed, however, very good breeding has been recorded where freely drained soils are fertile and wet peaty ground supports cotton-grass, e.g. Priestlaw and Misty Law.198
In red grouse and willow ptarmigan, predators, parasites and disease can reduce breeding success (see ‘Enemies’, below, and Chapter 13). Conversely, strong parental care, plenty of high-quality chick food and good weather can increase it.199 In a study of willow ptarmigan at Tranøy, Norway, and Lövhögen, Sweden, eggs robbed by predators accounted for much of the year-to-year variation in breeding success, while weather before hatching explained less of it (warm weather was positively related to breeding success, and rainfall was negatively related to it). Weather after hatching seemed less important.
When Howard Parker removed crows, ravens and magpies from half of the Norwegian island of Karlsø, willow ptarmigan bred no better and their densities in the next spring were no higher than on the half without removals.200 This occurred because stoats took a bigger percentage of nests on the half where he had done the removals, thus compensating for the absence of avian predators.
Average breeding success is often not associated with the average population density of breeding birds. In northeast Scotland, for example, high densities of red grouse often go along with poor or average breeding success, especially on infertile soils. On some peaty Scottish moorland, however, low densities often go along with big broods. Average population density is related to the amount of food and cover on an area, whereas breeding success depends largely on the quality of food for hens in spring and subsequently for their chicks. The two do not necessarily go together. The best average breeding success recorded has been from birds at low density but with high-quality food in spring, examples including red grouse at Priestlaw and Misty Law, and willow ptarmigan at Timansk, Karlsøy and Avalon (see Table 11).
ENEMIES
In Britain, man has created grouse-moors from forest, thereby benefiting red grouse. Man is also an enemy of grouse through hunting them, killing birds on
wires,201 by vehicles and in snares, destroying their habitat, polluting the environment and changing the climate. In North America and Eurasia, willow ptarmigan suffer from a wide array of predators, e.g. about 20 species take American adults or chicks.202 Fewer predator species live in Britain and Ireland than on Continental Europe, partly because man has extirpated the brown bear, wolf, lynx, sea eagle and goshawk, and exterminated red kites, polecats and pine martens on most land. On grouse-moors, gamekeepers kill most extant predators, and so some species are usually absent as breeders, such as golden eagles and hen harriers.
Unnaturally, many foxes and crows have become the main predators in Britain and Ireland, after man extirpated bigger predators that kill or compete with them (see Chapter 13). Man also created extra food for them, in the form of carcasses from overstocked sheep and red deer, waste food in rubbish dumps and tourist scraps, invertebrates on fields, road-kills, and animals killed by wires.
Foxes, wildcats, stoats and pine martens kill adult grouse, and along with weasels, crows, ravens and gulls they also take eggs and chicks. Hen harriers kill adults and chicks, as do golden and sea eagles, peregrines, sparrowhawks, goshawks and buzzards. Short-eared owls occasionally kill chicks, and we have known a hedgehog to raid a nest to eat a few eggs. The set of predators and prey that we now have is so human-influenced that their interactions are unpredictable and perhaps unprecedented.
Several parasite species live on and in Lagopus lagopus, and in some years threadworms kill many adult red grouse and result in poor breeding by others (see Chapter 13). The tick-borne louping-ill virus can cause catastrophic mortality of adults and chicks. Though still localised, it has spread since 1980 to more moors and to higher altitude, and threatens grouse shooting. It has unleashed controversies over high densities of deer as tick hosts, and the large-scale culling of mountain hares as carriers of the virus.
THE FUTURE
Most willow ptarmigan live on such remote land that their outlook should be bright in the near future, though man-induced pollution and climate change may alter this. Birds in the south of the range, however, have declined through the loss, deterioration and fragmentation of habitat by farming and forestry. In addition, red grouse have decreased owing to poor burning, and to overgrazing by red deer. Their abundance in years to come will depend largely on the future of heather moorland and whether it is maintained as grouse-moor or put to other use.
SUMMARY
The willow ptarmigan has the biggest range of any grouse, covering a vast area of tundra, scrub, open woodland and moorland. Numbers tend to fluctuate in cycles, whose period varies from three or four to about ten years. Red grouse, a subspecies of willow ptarmigan, are resident on moorland and do not turn white in winter. They reach high density on moors with a patchwork of short heather as food, beside tall heather as cover. Burning can produce this mosaic, but on the highest moorland a suitable mosaic occurs naturally because the windy climate keeps vegetation fairly short. Densities of willow ptarmigan are very low in the high Arctic and Kazakhstan, where food plants are sparse. Birds lay large clutches of eggs and rear large broods on land with nutritious food for laying hens. The best breeding so far recorded involved birds at low density with access to food of high quality.