Activity budgets and sociality in a monomorphic ungulate: the African oryx (Oryx gazella)

Abstract

Sexual size dimorphism in ruminants is associated with social and (or) habitat segregation, while monomorphic species often live alone, in monogamous pairs, or in mixed-sex groups. Most research on sexual differences in behaviour has been done on sexually size-dimorphic ruminants, whereas little is known about monomorphic species. We tested the activity budget hypothesis which predicts that similar-sized individuals should have similar activity budgets, while dissimilarly sized individuals should differ in their behaviours. We studied African oryx ( Oryx gazella (L., 1758)), which are size-monomorphic, to investigate how age, sex, or reproductive state affect their foraging behaviour. We expected that males and females have similar activity budgets, except for lactating females who were expected to spend slightly more time foraging. Younger, smaller animals were predicted to differ in their activity budgets from adults, owing to high energy demands. We predicted that air temperature, vegetation height, and group sizes would be more important in shaping activity budgets and feeding rates than sex or reproductive differences. The sexes did not differ in their behaviour, while subadults spent less time active than adults. Temperature and vegetation height significantly affected their behaviour. We discuss the importance of environmental, as well as intrinsic, factors when studying sexual differences in behaviour and habitat use.