Population dynamics, mating system and philopatry in a high altitude colony of alpine marmots (Marmota marmotaL.)

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Abstract
This study took place in the Parco Nazionale del Gran Paradiso (P.N.G.P.) from 1981 to 1993. Most of the observations were made from early June to late September. Marmots inhabited the concavities of the valleys above the timberline and on slopes from 0° to 35° of a transect of 4200 ha. Density was estimated by animal counts in two sample areas and ranged from 0.6 to 1.5 an/ha. Population dynamics was investigated from 1985 to 1993 in a colony at 2350 m; 57 marmots were live trapped for individual recognition. The total number of sexually mature reproductive groups observed was 27, in 18.5% a trio made of two unrelated males and one female was present. Never were two adult females found together and never were two different litters found concurrently on the same territory. Male/female ratio for immigration was 1.8, G test P > 0.005. Mean group size not including infants was 4.7 ± 2.9, range 2–11. Social groups had the highest turnover rate ever reported for a colony of alpine marmots. A total of 60 infants were born during this study. Mean litter size was 4 ± 0.65, and the median was 4. Mean number of litters sired per female was 1.5 ± 1.77. Forty percent of the new pairs disappeared after their first overwintering with a litter. Infant mortality, ascribed both to winter stress and predation, was 77.7% when both parents, or at least the mother only, was present the following summer. No sex difference for philopatry was found, and mean age length of residence in the natal territory was 2.29, range 2–3. Predation was documented on 8.77% of all individually marked animals.