In winter, snow and ice even prey upon the fauna of the Swiss Alps. While marmots retreat into their cosy burrows to hibernate, ibexes, chamois, snow hares and bearded vultures remain active even at the coldest time of year. They all have developed special abilities to withstand the barren, adverse conditions at altitudes of up to 3000 metres. In the Graubünden National Park, they remain undisturbed throughout winter, when the high mountain landscape is off bounds for all but park rangers and researchers.