Snow Bunting
How this winter delight adapts to a cold and harsh environment for survival is a fascinating tale
The fascinating tale of how the Snow Bunting adapts to survive in a harsh environment
Acouple of years ago, I climbed Ben Nevis with my son, Samuel. As the many who have done the same will testify, it is quite a trudge, especially on the zigzag section.
Our cause wasn’t helped by continually coming across a sadistic Yorkshireman, who kept on saying things such as “You’re not even half-way there yet.” He was still telling us there was a long way to go when we were, unknowingly, 10 minutes from the summit.
But once aloft, of course, on the patchily snowy plateau of Britain’s highest mountain, the usual mixture of adrenaline and delight overcame us, as it did for all the assembled throng on a late May lunchtime, who cheered themselves and clapped and even danced. And then another voice echoed across the scree; a quieter one, crystal-clear and sweet. It came from the Old Observatory Tower, where a Snow Bunting perched, resplendent in black-andwhite. Singer and song seemed perfect for the rarefied location, and occasion.
The Snow Bunting is an extraordinarily tough bird. The population of the Cairngorms is an outlier, with most other breeding areas well to the north, deep into the extreme Arctic. In fact, the Snow Bunting breeds as far north as any small bird in the world and may also winter in extreme conditions. It is large for a passerine, about 15cm long, and has particularly dense plumage. The tarsus is feathered, and the birds often go around assuming a distinctive crouched posture, which means they lose less heat
through the feet than they otherwise would. One of the Snow Bunting’s more extreme adaptations to cold is its ability to dig into the snow. Snow, of course, is relatively good for insulation, so digging a hollow in which to roost is a sensible precaution against dangerous conditions, especially at night.
Individuals will also loaf in their holes during the day. Wherever they occur in the Cairngorms, Snow Buntings do tend to gravitate towards snow patches, partly for this reason and partly for another.
When insects blown uphill by the wind land on snow, they are immobilised and are easy to catch. The nest, though, is carefully selected for the shelter it offers.
Nest building
Breeding Snow Buntings are typically found in rocky areas, even in nunataks, which are rocky ‘islands’ amidst ice-fields and ice-caps. They select a narrow crevice and build the nest right at the end of it, well out of view from the entrance and averaging 27cm from the outdoors.
The nest itself, as you might expect, is robust and has thick walls, made up from moss and grass. Other inner furnishings can be wonderfully reflective of the Arctic. Nests often contain the feathers of Ptarmigans, and sometimes Snowy Owls. Sometimes there is the fur of an Arctic Fox, or the wool of a Musk-Ox or Reindeer, all proven Arctic garb.
If there are no natural sites for the nest, Snow Buntings are more than willing to mix it with people and use their trappings. They are often found on the streets of Arctic villages, using the buildings. They will occupy empty cans and other human throwaway items. They also have a curious propensity to nest in skulls of carcasses, since these are often the right shape and relatively thick. It’s one way to get ahead in nest-building.
In common with other buntings, Snow Buntings change their diet when breeding. Here in Britain, we are used to seeing them in flocks eating seeds in winter, but in the Arctic, or in the mountains, they consume, in addition, insects and other invertebrates, which of course are found in profusion in the seasonally productive tundra, as many a human visitor finds to their cost. If you’re insectivorous it is almost impossible not to eat well – it is the reason that Snow Buntings venture into these Arctic
extremities in the first place.
By the autumn, though, the diet mainly reverts to a vegetarian one. These birds eat seeds in prodigious quantities, mainly those of weeds and grasses. During the winter, an individual Snow Bunting has been collected with 2,000 seeds in its stomach and crop, although 500-1,000 is more usual. When they go to roost, most Snow Buntings have enough food to last for a fallow day.
Energetic flocks
For most British birders, Snow Buntings are the ultimate winter delight, a species you might come across along the chilly, windswept coasts of the North Sea, Irish Sea and Scottish coast. They are found on sand dunes, saltmarshes and shingle, somehow eking out a living. They are famously found in energetic, highly mobile flocks, which often sweep past you on a wide-open beach in a flurry of white wings.
Once they do land, the birds never seem to settle, but instead move forward on a broad front. They move so quickly that birds at the back seem anxious not to be left behind, and leapfrog over their colleagues to get to the front.
As winter progresses, so the individuals in a Snow Bunting flock begin to change pattern, and the males, in particular, become smarter and whiter. They don’t moult their feathers at this time, as it would compromise their insulation, but instead they follow a trick practised by several other small birds. When they moult in the autumn, their feathers have dull tips and the fresh plumage has a muted look. However, the effect of wear and tear is to abrade away the tips of the feathers to expose the more colourful sub-terminal bands. Strangely, as the bird gets worn and scruffy, so it looks better.
Most of the Snow Buntings wintering in
Britain and Ireland hail from the breeding grounds in Iceland, although there is some evidence that some may come from much further afield, perhaps Greenland or even Canada. Whatever their origin, they remain until March or April before returning north.
There is a curious quirk concerning the return migration of Snow Buntings. While it is common among songbirds for the males to arrive on the breeding territory earlier than the females, the gap is usually only 10-14 days. In the case of Snow Buntings, however, it is much longer. Many males arrive a month before the females, and a few arrive six weeks earlier. This is an extraordinary difference. At first the males wander around in flocks, but after a couple of weeks they will start to form and defend territories. The birds returning to the High Arctic take a great risk.
Summer up there takes a long time to arrive. There is very little food, and many birds have to make do with raking through snow to get seeds. Snow Buntings have been seen contending with temperatures of -30°C. Physiological tests in the laboratory have shown that these birds start losing heat within an hour at -50°C, the point at which they cannot survive.
Why do the males arrive so early? It is thought to be related to the fact that suitable rocky clefts for the nests are always in short supply, and there is intense competition for them wherever they are found. The earliest arrivals can ensure that they lay claim to a good site.
Let’s just hope that, in the midst of an early spring storm, as the wind rockets around their snow-hole and the temperature plummets, a voice doesn’t tell them: “There’s a long way to go yet.”