Occupation of hibernacula, seasonal activity, and body size in a high altitude colony of Alpine marmots (Marmota marmota)

This study took place in the Parco Nazionale del Gran Paradiso (P.N.G.P.), Valle d'Aosta, Italy, from 1985 to 1993 on an area of 200 ha, 52% of which was a suitable surface for marmot settling during summer. Density of hibernacula varied from 0.09 burrows per hectare in 1986, to 0.2 burrows per hectare in 1991, the year when the maximum density of hibernacula was found. The mean number of hibernacula across years was 14.37, and the mean density was 0.13 per hectare. Despite a fluctuation of 10–21 hibernacula found in the springtime, the number of permanent hibernacula increased from 10 to 13. All new hibernacula that became permanent appeared within empty territories, suggesting that at least a fraction of the annual dispersers hazarded to dig new hibernacula or readapt summer burrows. Above the timberline, animals at higher elevation emerged later than animals at lower elevations (GLM; df = 1,21; F = 18.41; P = 0.000). Seventy-one percent of the infants distributed in 14 litters were observed for the first time above ground within a 10-day span. Infants weighed significantly less than reported in other studies. Mass of adult males was related to date of emergence during spring (GLM; Regression, F = 35.72; df = 1,9; P = 0.000). Mass of adult females was not related to date of spring emergence but only to presence or absence of lactation (GLM; F = 0.43; df = 1,11; P = 0.52; and F = 5.31; df = 1,11; P = 0.042, respectively for day from spring emergence and for lactational status).