Functions of female aggression during the pupping and mating season of grey seals, Halichoerus grypus (Fabricius)

Abstract

Aggression of female grey seals Halichoerus grypus toward conspecifics was studied during the pupping and mating season on Sable Island, N.S. The responses of 65 individually identified females with pups toward known males and females were recorded throughout each female's stage of lactation. Female aggression varied both quantitatively and qualitatively as a function of the sex of an approaching animal. Males were threatened more often than females even though females outnumbered males. The likelihood of females threatening other females was affected by the location of the threatening female's pup, but aggression towards males was not affected by the pup's position. Females responded aggressively less often in the second half of lactation, when both weaning of the pup and oestrus occur, than in the first half. They were also more likely to threaten transient males than tenured males. However, a male approaching or mounting a female, whatever his status, was more likely to be challenged by another male if the female threatened him than if she did not. These challenges generally interrupted a male's approach or mount and hence a potential copulation. The results are consistent with the hypothesis that female aggression during the lactation period helps to protect the pup and increases the likelihood that a female mates with a dominant male. This latter function may be viewed as a form of mate choice.