Sex/age differences in foraging, vigilance and alertness in a social herbivore

Antipredator strategies and social factors may influence vigilance behaviour in herbivores. Vigilance can differ between sex/age classes, but information is contradictory in the existing literature. We investigated sex/age differences of vigilance in fallow deer Dama dama, in a Mediterranean area. Females (>1year old) showed a lower proportion of time foraging and a greater alertness rate than males (1years old). Decrease of vigilance with increasing group size was observed for females and adult males, but not for young and subadult males, suggesting that group-size effects on vigilance were not consistent across individuals of different sex/age classes. Most likely, females tended to reduce the predation risk for their offspring through a comparatively greater duration and frequency of vigilance. Young/subadult males showed a greater alertness than adult males, which may depend on intraspecific competition in larger groups. Both antipredator and social factors could explain sex/age differences of vigilance in fallow deer.