Partial migration of roe deer in the Alps: patterns and climate dependence

Despite the abundant literature on behavioural ecology of roe deer, few studies have been carried out in the Alpine range, where the topographical complexity results in an impressive variety of habitats and climatic conditions along a relatively small spatial scale. In particular, winter conditions at high altitudes may be assimilated to those occurring in northern environments, where migrations of roe deer to wintering areas have been recorded. We captured and marked with GSM-GPS collars 29 roe deer (19 females and 10 males) in Monte Bondone area (Eastern Italian Alps, 500m-1700m a.s.l.), an isolated mountain range of about 150 km2, from January 2005 to November 2006. In winter, resident and migrant individuals occupied the same home ranges at the bottom of the valley, while in spring migrants moved to higher altitudes and stayed there until the first snowfall in autumn. Rather different behaviours were recorded in winter 2006-2007 (one of the mildest in the last decades): animals left summer areas only at the end of January, again after the first considerable snowfall. However, after reaching and occupying the wintering areas of the previous year, they moved back to summer areas as the weather stabilized, or repeated the migration route at all major weather changes. In all cases, migrations happened always along the same routes and within a 24 hours interval. Our study indicated that roe deer adapted to alpine conditions either occupying stable areas not subject to climatic extremes, or ranging in distinct wintering and summer areas. Migrant individuals showed great behavioural flexibility to climatic changes, preferring the areas occupied in the reproductive season as long as weather conditions (mainly snow cover) were not limiting to their survival. We are currently comparing trajectories of migrant and resident individuals, and of migrant individuals among the two years with contrasting climatic conditions, expecting to recognize different movement modes. We will validate our results with data from other European contexts, within the EURODEER collaborative project (http://sites.google.com/site/eurodeerproject/).