Home range size, foraging behaviour and risk of predation in Alpine marmots (Marmota marmota) [Taille du domaine vital, comportement d'alimentation et risque de prédation chez les marmottes des Alpes (Marmota marmota)].

Résumé

In hibernating mammals such as alpine marmots, summer body weight gain is one of the primary factors influencing overwinter survival. It has been shown that body weight gain of these animals is influenced by abundance and quality of food resources, and the exploitation of resources within their territories, leads marmots to feed away from the main burrow, increasing the risk of being predate upon (Holmes, 1984). In this study we investigated the trade off between home range size and body weight, testing the follow hypothesis: the less the individual weighs the more it risks feeding further away from the main burrow, in order to obtain higher energy intake (better food resources) despite the higher risk predation. We took observation during all summer 2007 on marked individuals of alpine marmots and we daily calculated the distances between foraging localizations from the main burrow and from the nearest burrow; the localizations, registered using a range finder, a clinometer and a goniometer, had been also used to calculate the individual home range size. The body weights ere been registered during the capture and with electronic scales at the entrance of burrows. The analysis reveals that only juveniles support our hypothesis. Spatial utilization was analyzed: every family group shares a common home range (1.048 ± 0.22 ha), slightly overlapped (9.3 ± 3%) to family with adjacent territories. When marmots forage, the distance from the main burrow is age-dependent; they reduce the distance from the nearest burrow in the afternoon: it could be due to differences in daily activities of predator or to different environmental conditions and other studies are nowadays working on these hypothesis. Moreover, the more the marmot lives and forages near the wood line, where vigilance is higher, the more it weights: this could be due to a possible trade off between an earlier snow-melting, which allows marmots to have access during a longer period to rich and abundant food resources, and an higher risk of predation. However this hypothesis needs more studies.