L'enneigement hivernal : un facteur de variation du recrutement chez l'isard (Rupicapra pyrenaica pyrenaica)

Abstract

To assess the relationships between winter climatic conditions and population dynamics of mountain ungulates, we monitored over the long term an unhunted isard (Rupicapra pyrenaica pyrenaica) population living in the Pyrénées National Park. We used general linear modelling to assess (i) the influence of the observation date (between November and April) of the transect sampled and of the year on population recruitment (proportion of females 2 years of age and older with kids at heel) and (ii) the impact of snow accumulation during winter (cumulated snow fall from November to April) on kid mortality. As expected, the mean number of kids per female decreased over the observation period. The mean number of kids per female showed marked among-year differences in initial recruitment (measured on 31 October) as well as in kid mortality (measured as the decrease in recruitment between 31 October and 31 March). This model accounted for 80% of the variability observed in the field data. Among-year differences in snow accumulation accounted for most (86%) of the yearly variation observed in kid mortality. Our study demonstrates that winter snow may severely affect juvenile survival, and thereby population dynamics of mountain ungulates.