Seasonal movements 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. This study aimed at assessing seasonal home ranges and movements of individual roe deer by GPS telemetry in an Alpine area, with particular regard to the effect of climatic parameters. Captures were carried out 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. 29 roe deer (19 females and 10 males) were captured and marked with GSM-GPS collars (Vectronic GPS-Pro 1D) and data were collected every 4 hours, for approximately 50 thousands locations in total. Size of annual home ranges (kernel 90%) did not differ between sexes, but it strongly did between resident and migrant individuals. The former occupied the same areas throughout the year, while the latter moved in spring to sites at higher altitudes than wintering ones, between 1 and 6km far. Both in 2005 and 2006, spring migrations took place at various times for different individuals, before the end of May. In 2005, all individuals moved to wintering areas right after the first abundant snowfall: they occupied the same home ranges than the winter before until the following spring. A rather different behaviour was recorded in winter 2006-2007, which was declared to be the milder of the last century: 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; they repeated the same behaviour 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 parameters (mainly snow cover) allowed so.