Dispersal patterns alpine marmots (Marmota marmota) [Patrons de dispersion chez la marmotte alpine].

Résumé

Alpine marmots (Marmota marmota) live in social groups consisting of a territorial pair and up to 18 lower ranking animals of various ages, mostly the pair's offspring. In each group the dominant male and female defend the group' home range against same-sex adult intruders. Among females, reproduction is restricted to territorial animals. In contrast, subordinate males are not enterily excluded from reproduction. Marmots may become terrotorial (i) by evicting a territory owner, or (ii) by taking over a vacant territorial position, either at home or after dispersal in other territories. Dispersal patterns of mature subordinate alpine marmots were studied in the Berchtesgaen National Park, Germany, from 1982 to 1996 with behavioural observations, life-trapping and telemtry. Only long-distance dispersers (>500 m, n=22, mortality: 31.8%), but not short-distance dispersers (<500M, n=20, 5.0%) had much higher mortality risk during summer than those staying in their group as subordinates (n=75, 2.7%, p=0.002). In this investigated male biased population (sex-ratio at weaning 1.5:1, n=464, p<0.005), females became territorial closer to their home territory than males. In both sexes the distance of ressettlement did not affect (i) winter mortality after dispersal, (ii) the time period in territorial position, or (iii) reproductive success. This sex-biased dispersal pattern may be a consequence of the stronger competition among males for territorial positions and the high mortality risk in long-distance dispersal.