Evidence for a breeding dispersal tactic in a large herbivore

From an evolutionary stand point, breeding dispersal, the net movement between successive breeding sites, remains a poorly understood and seldom reported phenomenon, despite its potential importance for population dynamics. This is particularly so for mammals, however, recent descriptive data from several species of large herbivore indicate that females may be unusually mobile during the breeding season, undertaking short trips outside their normal home range. We suggest that if fertilisation occurs during these exceptional forays, then this behaviour could be considered as a form of breeding dispersal, at least from a genetic point of view. This behaviour could be motivated by inbreeding avoidance, the search for good genes and/or multiple paternity. We illustrate this by investigating the ranging behaviour of GPS-monitored adult roe deer from six intensively studied populations across Europe. We show that excursions are common from June to August, with almost half of females making at least one excursion. Excursions are concentrated in time and centred on the rutting period, indicating a link with reproduction. The distance females travel during excursions was significantly greater than the diameter of an average male home range, while travel speed decreased as the female progressed beyond this diameter, indicating searching behaviour or interaction with other male(s) outside the resident male’s territory. Because adults of both sexes are normally highly sedentary, the potential for mating with relatives is substantial; hence, we conclude that rut excursions could be an alternative tactic enabling roe deer females to avoid mating with a closely related male