Still to be found on the peaks of the Cairngorms, and other mountains in northern Scotland, can be found one of the hardiest of British birds, the Rock Ptarmigan Lagopus muta. Once found in the Lake District in England and the Southern Uplands in Scotland, this is a relict species, surviving from the last Ice Age. Widespread outside the UK, with a circumpolar distribution, it is basically the northern replacement for the Willow Grouse, living in barren, treeless landscapes of the tundra. South of the Arctic, the changing habitat as the world warmed up after the last glaciation marooned populations on the peaks of various mountains far to the south of its main range, where the bitter winds and cold winters that it is adapted to survive still gave it an edge against competitors.
As with all grouse, it is a specialist, at least as an adult, on plant parts, especially the buds and catkins of the creeping Arctic Willow Salix herbacea and Arctic Birch Betula nana. The chicks feed on insects at first, which provides them with the protein they need to grow fast in the short summers. As with Willow Grouse, they are quite sedentary birds, and this combined with fragmentation of their habitat between different mountain ranges has resulted in differentiation between the isolated populations, with 20-30 different subspecies being named.
Readers of last weeks post will remember that Willow Grouse outside the UK change colour in winter, but unlike the endemic British subspecies of Willow Grouse, the Red Grouse, British Ptarmigans still retain the colour changing habit, moulting from a mottled brown plumage in summer to pure white in the winter. This is of course for camouflage, and helps to conceal them against the snow from their natural predators, which in the UK are Golden Eagles and Stoats (which also turn white in the north of their range). Further north in the Arctic Ptarmigan are important prey for Gyr Falcons, which would have been present in the UK during the last glaciation but are now no longer resident breeders.
Winter plumage Ptarmigan
Ermine (stoat in winter coat)
Ptarmigan in the UK are hunted on some game estates in Scotland, but the numbers taken each year are comparatively few as the main grouse shot in Scotland is the much more numerous Red Grouse. Despite their restricted habitat, Ptarmigan are not particularly rare where they are found, and the UK population is estimated at around 10,000 pairs. This conceals considerable year on year variation though, as the extreme climate where they live can vary considerably during the breeding season, resulting in great fluctuations in breeding success. For the UK population, the greatest ongoing threat is climate change, with warming climate on the high peaks altering the habitat to a degree they cannot tolerate. Another man-made threat is litter left behind by hikers, as this attracts and sustains crows, which also prey on ptarmigan chicks. Ptarmigan also carry the debilitating strongylosis parasitic worm, but tend to carry a much lighter load than Red Grouse, probably because the latter live at much higher population densities.