Strategies for survival
March 2010
Mountain hares have a more rounded shape and shorter ears than the brown hare, for better heat retention. Photo: Stuart Rae
by Stuart Rae
The high ground in the Cairngorms forms the largest expanse of near-arctic habitat in Scotland. There is snow there every winter; and spring, summer and autumn are short. Summer can even be dry. Cold temperatures, deep long-lying snow, wind and desiccation are the norm. Yet animals and plants survive these conditions by a variety of wonderful adaptations of habit and form.
Snow can restrict animals such as mountain hares and ptarmigan from reaching their food if it lies too deep and firm, although usually it is blown clear of the ridges exposing ample food. Cold and snow go together, but snow can be a useful defence from excessive cold by forming a physical barrier from the wind and frost. Fresh dry snow is blown into snow beds which can lie firm for months, well into summer and some can last right through to the next winter. The temperature does not usually drop much below -5oC under a snow bed, and wind-chill is excluded, so any plants or animals below the snow are protected from very low temperatures and wind-chill. Ptarmigan roost in snow holes. A flock will settle on a snow bank and burrow in out of the wind; one hole per bird, each hole used only once. The mountain hares dig forms into snow too.
Ptarmigan and mountain hares moult into white feathers and fur in winter. This is not only for camouflage to avoid detection by predators when on snow; their winter plumage and pelage are thicker and better for heat retention than their dark summer ones. Both species are slightly smaller than their near relatives, the red grouse and brown hare, with shorter legs and in the case of the hares, ears and face. And when at rest on a cold day both tuck themselves into a round shape, so reducing surface area loss of heat. Many of the best adaptations to living in the cold are this subtle.
Furry plants? Numerous alpine/arctic plant species such as alpine mouse-ear and dwarf cudweed, a relative of edelweiss, have tiny hairs on their stems, leaves and sepals, thousands of them – though not on the petals which are short-lived. The hairs help to reduce heat loss, desiccation and damage by wind which is critical to arctic dwellers.
All plants on the true high ground, especially on the plateaux are short. The natural tree line, the altitude where trees cease to grow, is about 650m, although the trees growing at that height are usually stunted and twisted by wind. As with the animals, small size is important for the plants’ survival up on the hilltops. This enables them to lie under even thin coverings of snow, and so gain some protection from it. The plants lie dormant under the snow, adapting various traits in growth and form for survival.
Voles and shrews live there too, the former building runs and nests in the dry grasses which are revealed by later thaws as miniature hayricks and stacks.
Blaeberry – a favourite food of ptarmigan
Various species of plants can tolerate snow lie more than others. Some such as blaeberry, a favourite food of ptarmigan, benefits from being covered for months by snow as it is protected from being eaten all that time. However, creeping azalea, which ptarmigan can eat but is less favoured, grows profusely on wind-blown ridges where snow seldom collects. This plant of the wind-swept stony ridges has evergreen leaves, waxy on the topside, furry on the lower – all adaptations which help plants to survive in a cold windy habitat.
The azalea and heather are the more common plants on the dry stony ridges. They spread long stems downwind, fully prostrate, although only a few centimetres tall, in the lee of the wind-scoured boulders and stones.
Our upright human posture is not at all well adapted to cold windy weather. Keeping low is one of the main strategies employed by arctic/alpine wildlife. Standing six feet tall on a windy hilltop, exposed to debilitating wind chill and physical hurt from flying ice particles and gravel is not a comfortable experience.
Appropriate behaviour is basic for survival on the plateau. Mountain hares lie up during windy days in forms, summer or winter. These are just like those of their brown cousins in the lowlands, and the same sites are used over years. They probably have been for thousands of years, all snugly set to avoid the prevailing winds.
Some plants, such as the alpine lady’s mantle, hide in niches, too, and can grow much taller, well a few centimetres so, than their neighbours growing out in the open nearby. Other plants growing in the open have adapted a tight cushion form, like the moss campion, their dense walls of leaves providing shelter and a warmer micro-climate to the core of the plant.
Most plants up there are perennial. That allows them to gather nutrients in one year and set buds, which are ready to burst open upon the first days of the following spring and so set seed quickly in the short summer. Purple saxifrage can flower while the snow is melting around it. Alpines usually have small flowers and one of the more delicate plants, heath bedstraw, has the tiniest of petals yet is widespread, growing beneath the taller heath on the lower slopes and in tiny form amongst mosses on the barest plateaux.
Extremes in weather are part of the mountain environment. Certainly it can be cold in winter – or summer – but it can also be warm in summer. Plants or animals living in marginal alpine-arctic conditions need to survive summer stress as much as winter and as there is little snow in summer to protect them from desiccating winds; drought can be a killer. Plants will die back and not set seed in warm summers.
Desiccation is a real problem, and snow can be a saviour once more. Long-lying snow beds act as reservoirs, slowly releasing water to a luxuriant growth of alpines around their seepage lines. Insects are also abundant around these wells, and together with numerous bird and hare droppings, they indicate their similar value to the animals.
Snow for survival – the big picture
In the 10,000 years or so since the last ice sheets retreated from the Cairngorms, the plants and animals that are best suited to the alpine/arctic habitat of the high hills have become established. They not only grow better there than other species, they need snowy weather for their survival. And it is the whole, the big picture, the variety of landforms, the range of plant and animal life and the weather, especially that of the arctic/alpine zone, which makes the Cairngorms so exceptional in Scotland.
The Cairngorms are grand; they and their wildlife knock our puny human lifestyle into scale. Cosy in our urban homes and workplaces, we have forgotten how to live in winter weather. The animals and plants haven’t, though, and the range of methods they have adapted to not only live, but thrive in such conditions is fascinatingly varied. We can learn from their strategies for survival in the hills.
Is snowy weather ‘bad’ weather, or is that merely an anthropocentric adjective? We have lost contact with the wild and think of weather in terms of our short life-experiences. This is a dynamic world which is continually changing. Last winter was just a little reminder.
Stuart Rae grew up in Aberdeen and has been working on wildlife of the Scottish hills since the 1980s. He studied ptarmigan for his PhD at the University of Aberdeen, and incorporates climbing and nature photography to his days on the hill whenever possible.
This is an article from the March 2010 edition of Leopard Magazine. To read much more like this every month, see our subscription details.