Foster & Dagg, 1972; van der Jeugd & Prins, 2000) and in open areas or areas with short vegetation (Foster & Dagg, 1972; Young & Isbell, 1991), a pattern consistent with our observations in Serengeti. Bercovitch & Berry (2010) suggested that in open terrain, increasing herd size does reduce predation risk for giraffes. In mountain sheep, similar behavior is observed: females and offspring occupy areas where they can detect and evade predation, while Dasatinib mouse males occupy high-risk areas where they are more likely to encounter predators (Bleich, Bowyer & Wehausen, 1997). Consistent with this idea, claw marks were rarest in
Kirawira, where giraffes commonly gather in large herds in open grassland areas. Although we did not find any relationship between an individual’s mean herd size and claw-mark presence
in Seronera, mean individual herd size may not be a useful measure if individuals are only likely to be attacked when temporarily alone. If adult females generally behave in less risky ways, then why do they have the highest claw-mark prevalence? High claw-mark prevalence in adult females could be partially explained by marks acquired during calf defense. In a study of bottlenose dolphins Tursiops truncatus, Corkeron et al. (1987) observed fresh predation marks on a relatively high number of females with calves, and they suggested that female–calf pairs are more vulnerable BGB324 cost to predation. Giraffe calves are an attractive target for lions. Mothers protect their calves by positioning them between their legs and by chasing or kicking at predators (Pratt & Anderson, 1979; Dagg & Foster, 1982). Lions have been observed lunging at nursing females to distract them from their calves, and this may be when they inflict superficial claw marks. In support of this hypothesis, we found a substantial jump in the prevalence of claw marks
among females at age 4–5 years, coincident with the onset of first parturition (Fig. 4a). Injuries incurred during calf defense could also explain why only nearly adult female giraffes were observed with marks on 4 or more body regions. In addition, the only observation of an individual surviving more than 1 non-lethal attack was that of an adult female. Observations of fresh claw marks on nursing females would provide additional support for this hypothesis. Adult females may be most susceptible to lethal lion attacks in the last weeks of pregnancy and just after parturition, when females behave more like mature males: pregnant females spend more time browsing in dense vegetation to meet nutritional needs (Young & Isbell, 1991). Females also become solitary shortly before giving birth (Foster & Dagg, 1972; Strauss, pers. obs.) and keep their neonates relatively isolated from other giraffes for up to 3 weeks post-partum (Langman, 1977; Pratt & Anderson, 1979; Mejia, in Moss, 1982), thereby forgoing the vigilance benefits of additional herd members.