Time budgets and foraging in a Malagasy primate: do sex differences reflect reproductive condition and female dominance?

Abstract

Female mammals commonly employ behavioral tactics of modulating activity levels and foraging behavior to counter the energetic burden of reproduction; these behavioral changes are reflected as intersexual differences. Traditional views of Malagasy primates posit that high reproductive costs select for female dominance which guarantees to energetically stressed females priority of resource access. I tested predictions regarding reproductive influences on sex differences in time budgets and foraging behavior using two groups of Milne-Edwards' sifaka (Propithecus diadema edwardsi) in southeastern Madagascar. Compared to males, females increased neither feeding nor resting time during gestation or lactation. Sex differences were essentially absent in all foraging time variables examined (time, duration, rate). In contrast, dietary composition diverged between the sexes in some months. The possibility that females selected particular food items to boost nutrient and energetic intake to meet increased requirements during reproduction must be further clarified with nutritional analyses. Sex differences in plant part choices coincided with lactation in one of the two study groups. Thus, the timing of sex differences in feeding patterns of P. d. edwardsi only partially supports the prediction that sex differences are most pronounced during the period of greatest female energetic demand. A comparative review indicated no tight association between female dominance and sex differences in foraging among Malagasy primates. Traditional female dominance theory falls short of explaining the observed patterns. The results of my study coupled with recent evidence suggest that non-behavioral tactics involving energy conservation and storage require further attention as mechanisms by which female lemurs cope with reproductive costs.