MATERNAL INVESTMENT IN MOUNTAIN BABOONS AND THE HYPOTHESIS OF REDUCEDCARE

It has been argued that female mammals should terminate expensive form s of infant care earlier as habitat quality declines. More recently it has been shown that among a variety of mammalian species, early termi nation of care is also associated with highly favourable conditions. I n this paper we present data on maternal investment decisions among ba boons (Papio cynocephalus ursinus) inhabiting the Drakensberg Mountain s of South Africa, and compare these with data from East African baboo n studies. Mothers in the mountain habitat face a set of environmental conditions where the problem of resource allocation to offspring is e xpected to be particularly acute. We begin by using the model of Altma nn (1980) of maternal time budgets to demonstrate that mountain baboon mothers experience greater perturbations to their activity budgets wh ile suckling than do mothers in other populations. They also provide c onsistently greater levels of care to their infants and do so in the a bsence of any form of overt conflict over access to the nipple. Althou gh this investment results in a relative lengthening of the interbirth interval (IBI), it is accompanied by relatively higher infant surviva l. We argue that factors that influence the maternal strategy adopted by mountain baboons include slow infant growth rates and a lack of pre dation in the habitat which influences probability of offspring surviv al beyond the immediate postnatal period. We suggest that both ''care- dependent'' sources of mortality (e.g. female reproductive condition, the amount of milk transferred to offspring) as well as ''care indepen dent'' sources of mortality (e.g. predation, infectious disease) shoul d be considered in studies of parental investment.