The developmental behavioural ecology of infant baboons (Papio cynocephalus ursinus)

Abstract

Presented in this thesis are the results of a 23-month field study (April 1991 - February 1993) which focused on infant development in a free-ranging baboon troop (Papio cynocephalus ursinus) inhabiting the Cathedral Peak Reserve in the Drakensberg Mountains, Natal Province (South Africa). The troop selected for study was, in demographic composition, representative of the greater Drakensberg baboon population. During the course of the study, five infants were born into the troop. At the end of the data collection period, the infants ranged in age from II-months to 17 -months old. The data presented are extracted primarily from 2678 half-hourly scan samples, representing approximately 1340 hours of observation. Data presented in this study indicate that baboon births in the Drakensberg are seasonally timed such that mothers are afforded some measure of relief from the energetic costs associated with intense infant dependency, particularly during the first few months postpartum. However, the timing of births is not optimal in terms of the development of infant nutritional independence. This has implications for the interbirth interval (38.4 months) which, for the Drakensberg females, is substantially longer than that for comparative studies, while the rate of infant survivorship through to 12-months (95%) is considerably higher than for other baboon populations. The development of independent feeding for the Drakensberg infants is, when compared with infants from other studies, considerably slower. The delayed transition to independent feeding which was observed is explained with reference to seasonally variable ecological conditions in the Drakensberg which necessarily resulted in infants remaining nutritionally dependent on mothers for a longer time than would normally be expected. The relationship between dependent and independent feeding, as alternate infant strategies, is considered within the context of weaning and its role in the iv promotion of independence. A model which purports to delineate the weaning period with reference to the rate of decline in various measures of maternal investment is applied to the data for this study, as well as for comparative studies. No clear consistency is evident in the rate of decline across the various measures for the present study. The trajectories of infant behavioural development toward the adult model of independent activity are described and considered. With the exception of nutritional independence, all other trajectories of infant behaviour followed similar developmental patterns to infants in comparative studies. Thus the appearance of particular behaviours, and the age at which transitions to independence were made, confirmed a general baboon pattern. The implications and consequences of delayed feeding independence for changes in behavioural development are considered within the context of general activity budgets. Data are also presented which examine the contexts within which adult males interact with infants. These data are considered in relation to the possible functional purposes served by male interaction with infants, as well as in terms of the effect male interaction with infants has on inter-male interaction. The data indicate individual male variability in both the extent and contexts of interaction with infants.