Territory defence in male European roe deer (Capreolus capreolus)-a sexual ornament?

The function of male territoriality in roe deer has been debated for decades. There now seems to be consensus that it is a mating tactic. As such, it is highly untypical though. The reasons being, first, males neither conform to the typical 'resource defence' territoriality model nor to the 'mate defence' territoriality model; second, territory defence commences several months in advance of the breeding season; and third, the territorial system seems to be very rigid, as practically all studies that have described the social organisation of the species have reported adult males to be territorial. In spite of the general agreement that territoriality is a mating tactic, conclusive evidence on which selective forces are responsible for the prevalent pattern is still lacking. In the present paper, it is suggested that territorial defence serves as a sexual ornament, i.e. 'cleanness' of other males on the territory, in combination with size of the 'clean' area, and tenure length are parameters used by females to estimate male phenotypic quality. The hypothesis generates at least four predictions, and available data provide support. It is concluded that although a firm test of the hypothesis remains to be undertaken, existing data support this, just as well as any other, explanatory model and therefore it should be taken into consideration.