Alpine mountain hares are a glacial relict species in the Alps and can be found between 700 and 3800 m a.s.l.. They show a coat colour change from brownish in summer to white in winter. The white fur provides camouflage and a better insulation, likely increasing winter survival. We hypothesise that the seasonal phenological timing of the coat colour pattern is under high selection pressure as observed in the related snowshoe hares and that the pattern is adapted to the environmental differences along an altitudinal gradient characterised with increasing snow cover duration. To test our hypothesis, we used data from regular hunting in the Canton Grisons, where about 1000 mountain hares are harvested every year. Hunters were asked to report the day and altitude of their hunting bag and to provide a photograph of the shot individual. Photographs were used to estimate coat colour (in % white). We collected datasets of 235 shot hares between 2012 and 2016 during the hunting season in autumn (October-November). The altitudinal range was between 1250 and 2960 m a.s.l. Coat colour was analysed in relation to calendar week, altitudinal class and bio-geographical region. Our results reveal strong relationship of coat colour moult pattern and altitude, with earlier change into white fur at higher altitudes. The results are discussed in the light of global warming with shorter snow cover duration, genetic diversity and adaptability in highly fragmented populations and additional threats by European hares (L. europaeus) moving to higher elevations and heavy winter tourism.