British Wildlife of the Week
The Scottish Cairngorms must surely be one of Britain’s harshest environments. Living in this spectacular mountain range, which was chiseled by glaciers and rainfall for millennia, truly is a battle for survival each and every day. Howling winds gust over the frozen plateaus. Conditions can change rapidly and dramatically – a relatively calm day can quickly deteriorate into a white-out. And as winter tightens its grip in this region, temperatures can drop to -20°C or below.
One of the few animals that is supremely adapted to this extreme habitat is the ptarmigan. Globally, this bird is found primarily in arctic and sub-arctic regions across Eurasia and North America. During the last Ice Age, when conditions were more to their liking, this species was widespread throughout continental Europe. Today, however, only a few isolated populations remain, and in the British Isles it is now confined to the remote Highlands of Scotland – our last remnant of sub-arctic climate.
A true cold-climate specialist, the ptarmigan is unquestionably Britain’s toughest bird. Unlike most other mountain birds, which head down to lower altitudes for the autumn and winter, ptarmigan spend their entire lives in this inhospitable environment, buffeted by the howling winds. Even when blizzards scour the summits, these hardy grouse stay put.
This is because the ptarmigan is fully kitted out for winter survival. Firstly, it has a double-coat of feathers. The inner coat traps the heat while the outer coat of longer feathers keeps out the wind and snow. The ptarmigan also has feathers everywhere – on its legs, the soles of its feet, even on its eyelids. All of this protection results in virtually zero heat loss. In winter, it survives by feeding on berries and plant shoots, and it is able to withstand the unforgiving weather by digging holes in the snow using its feet and hunkering down until the storms are over.
A plump, tasty grouse like the ptarmigan is on the menu of a lot of predators. To make matters worse, it is a ground-dwelling bird – and a very exposed one at that. In the wide, flat, treeless Arctic tundra, there is virtually nothing to hide behind. At least in the Cairngorms, there are rocks and boulders to provide cover. Even so, the ptarmigan relies heavily on camouflage to avoid being seen, blending in with the surrounding landscape. The problem with this is that the habitat changes drastically throughout the year. During the winter, mountainous regions and the tundra are both covered in thick snow, but in the summer months, the snow has melted, revealing low-lying vegetation and lichen-covered boulders.
The ptarmigan must therefore use seasonal camouflage, changing its plumage appropriately as the year progresses. In the winter, a ptarmigan is pure white and virtually invisible against the snow and ice. But that all-white plumage is not effective camouflage when the snow starts to melt. In fact, it makes the bird more conspicuous. So as the season continues, the ptarmigan loses its white feathers and starts to acquire reddish-brown ones to match the vegetation as it emerges from beneath the snow.
By the time summer has arrived, the birds have moulted most of their white feathers and are a rich mottled brown (though the males still retain a largely white underbelly). In autumn, they moult again, becoming as grey as the boulder-strewn landscape around them. Then, as winter once again approaches and the land becomes blanketed in snow, the ptarmigan must regrow its white feathers if it is to avoid being seen.
In the next British Wildlife of the Week, we’ll be looking at a winter visitor, one that hundreds of years ago was believed to have a very curious connection to a particular kind of crustacean – the barnacle goose.