Pity the poor mountain pygmy possum. Not only is the diminutive marsupial at risk from global climate change, feral cats and arsenic-carrying moths, it also is having its winter hibernation disturbed by the thud and thump of skiers and snowboarders in Australia's Snowy Mountains. Normally the possums hibernate during winter under a blanket of snow, waking up every seven to 10 days. Now research suggests they are being disturbed more frequently than that, leading to a dramatic fall in their numbers. Studies indicate waking up early uses valuable energy, reducing the tiny marsupials' chances of surviving the colder months. 'Skiing and snowboarding over the snow is like squashing down a duvet - it gets rid of the air in the snow and therefore the insulation. The best ski areas coincide with the best possum habitat - they both favour south-east facing slopes, which hold a lot of snow,' said Dr Linda Broome, senior officer for threatened species with the New South Wales National Parks and Wildlife Service. Dr Broome has been monitoring pygmy possum numbers at several ski resorts since 1986. At one, Mount Blue Cow, the population fell last year from 16 males and 38 females to two males and 12 females. At another resort, Charlotte's Pass, the resident colony has decreased by one third since 1997. Mountain pygmy possums, which are 10cm long, are among the most endangered of possums. They live only in a small area of alpine habitat straddling the border of New South Wales and Victoria in south-eastern Australia. There are believed to be about 2,000 adults, three-quarters of which are female. The animal also is at risk on other fronts. There have been unusually low numbers of its main prey, bogong moths, for the past two years, for reasons not fully understood. It may be that the moths are absorbing arsenic used in fertilisers and pesticides, which is then passed on to the possums. In the long run, the biggest threat is global warming. 'A temperature rise of just one degree could wipe out the population altogether,' Dr Broome said. As the Australian winter approaches, ski resorts are planning to run a campaign encouraging people to stay away from the possums' habitat. One resort, Perisher, will rope off about 10 hectares of ski slope where the creatures are known to hibernate. Meanwhile, Dr Broome will continue to monitor the population and has presented a species recovery plan to the New South Wales Government. Not all is gloom and doom, however. 'They have a good capacity for recovery and the females can have four babies a year,' Dr Broome said. 'Given the right conditions they can bounce back.'