Why Does That Mountain Animal Make Hay? Winter Lasts and It Does Not Sleep

The animal is a small round-bodied mammal with short limbs, no visible tail and rounded ears, weighing roughly a hundred and fifty grams, and although it looks like a rodent it belongs with rabbits and hares. Around thirty species are distributed across the mountains and steppes of Asia and western North America. They live in the gaps between broken rock on scree slopes and boulder fields, which provides shelter from predators and from temperature extremes, and they forage in the vegetation immediately around those rock piles rather than travelling any distance from cover.

The behaviour that defines them follows from not hibernating:

• •Vegetation is cut and carried back to the rocks in the mouth
• •It is spread in the sun to dry before being stored
• •Drying prevents it rotting or heating in the pile
• •A pile can reach several kilograms, far more than the animal weighs
• •Building it occupies most of the short summer
• •Piles are defended, and neighbours steal from each other

The animal is adapted for cold in a way that leaves almost no margin at the other end, carrying a dense coat and a high resting body temperature that sits only a few degrees below what is lethal to it. It cannot lose heat effectively and dies within hours of exposure to temperatures that a person would find merely warm. That forces it to retreat into the rock pile during the middle of a summer day, which removes exactly the hours it needs for gathering, so warming summers reduce foraging time rather than only causing direct heat stress. It also cannot disperse across warm valleys, so populations are isolated on separate mountains.

The animals are far easier to hear than to see and the calls carry a good deal of information. A short sharp bleat is given when a predator is spotted, and the response of neighbours to it has been studied in detail, showing that individuals distinguish calls from familiar neighbours and from strangers. Longer songs are given by males in the breeding season and during the autumn haymaking period, and are audible across a valley. The calls also mark territory, since a haypile represents an entire winter of food and is worth defending, and much of the summer noise is neighbours announcing that they are present and watching.

The animal has become a standard case study in climate-driven range shift, and the evidence is unusually good because the sites are documented. Surveys revisiting locations recorded in the early twentieth century have found populations gone from a substantial proportion of them in parts of the American Great Basin, with losses concentrated at lower elevations and on warmer slopes. Where populations persist they have generally moved upslope, which works only until there is no more mountain. Against that, the picture is not uniform, and populations survive in some unexpectedly warm places including low-elevation lava fields, where deep rock crevices provide cool refuges regardless of the air temperature.

A small relative of rabbits living in mountain rock piles stays active through winter instead of hibernating, so it spends the short summer cutting vegetation, drying it in the sun and stacking piles heavier than itself. Its dense coat and high body temperature leave almost no tolerance for heat, so warm afternoons drive it into the rocks and cost it foraging time. Populations have vanished from many lower sites.