Instability and diurnal variation in size of winter groupings of field roe deer

Abstract

The European roe deer (Capreolus capreolus) makes up unusually large winter groups in the cultivated plains it has colonized for some decades. In this paper, we investigate the instability of these groups, as well as the possible variations of their average size in the course of the day. The groups observed over at least 3 hours appeared largely unstable : half of them had broken up or fused with another group after 2 hours 38 minutes. Group fusion generally resulted from the spontaneous attraction between groups whose members had perceived one another. Most breakups resulted from the departure of one or more individuals, without any previous visible interactions between group members. Fusion was more frequent than breakups during most of the day. Subsequently, mean group size was larger in the hours before sunset than in the hours following sunrise. The results obtained are globally consistent with the assumption according to which group instability and the increased possibility of perceiving congeners are responsible for the unusually large winter groups made up by roe in cultivated plains.