SEX-DIFFERENCES IN GIRAFFE FORAGING BEHAVIOR AT 2 SPATIAL SCALES

We test predictions about differences in the foraging behaviors of mal e and female giraffes (Giraffa camelopardalis tippelskirchi Matchie) t hat derive from a hypothesis linking sexual size dimorphism to foragin g behavior. This body-size hypothesis predicts that males will exhibit specific behaviors that increase their dry-matter intake rate relativ e to females. Foraging behavior was examined at two hierarchical level s corresponding to two spatial and temporal scales, within patches and within habitats. Patches are defined as individual trees or shrubs an d habitats are defined as collections of patches within plant communit ies. Males were predicted to increase dry-matter intake rate within pa tches by taking larger bites, cropping bites more quickly, chewing les s, and chewing faster. Within habitats, males were expected to increas e intake rate by increasing the proportion of foraging time devoted to food ingestion as opposed to inter-patch travel time and vigilance. T he predictions were tested in a free-ranging population of giraffes in Mikumi National Park, Tanzania. Males spent less total time foraging than females but allocated a greater proportion of their foraging time to forage ingestion as opposed to travel between patches. There was n o sex difference in rumination time but males spent more time in activ ities other than foraging and rumination, such as walking. Within patc hes, males took larger bites than females, but females cropped bites m ore quickly and chewed faster. Males had longer per-bite handling time s than females but had shorter handling times per gram of intake. With in habitats, males had longer average patch residence times but there was There was no overall difference between sexes in vigilance while f oraging, although there were significant sex by habitat and sex by sea son interactions. Although not all the predictions were confirmed, ove rall the results agree qualitatively with the body-size hypothesis. Se x-related differences in foraging behavior led to greater estimated in take rates for males at the within-patch and within-habitat scales.