BEHAVIOURAL AND PHYSIOLOGICAL RESPONSES TO ANTHROPOGENIC FOOD SOURCES IN CHACMA BABOONS

Abstract

Human impact on primate habitats is increasing across the range countries. As a result, many primates are sharing their habitats with humans. This proximity to humans is often accompanied with the incorporation of human foods into primate diets. The effects of human foods, and how primates modify their behaviours and physiology according to these changing food habits, are therefore becoming increasingly important to understand. This study aimed to increase our understanding of the impacts of human foods on primates by studying a baboon group that feeds on a human rubbish dump, investigating their behavioural plasticity and physiological changes.
This study was conducted on a habituated chacma baboon (Papio ursinus) group in Alldays, South Africa. The group regularly visits a garbage dump from where they gained food on a daily basis. Behavioural (activity budget, ranging distance), physiological (glucocorticoid and thyroid hormone levels) and ecological (food availability) data were collected over a 12-month period. A novel method combining the estimated number of dumped bags and sampling of their content, was used to estimate dump food availability. Similar data on other baboon groups from across the African continent, both wild-feeding and anthropogenic foragers, were compiled from the literature to enable comparison of the impacts of dump-feeding.
The study results showed that the activity budgets of the Alldays Dump Group were dominated by resting, which was significantly higher than wild foraging baboons; whereas feeding time was significantly lower than for both wild foraging and other anthropogenic foraging baboons. The group spent an average of three hours per day in the dump, which varied according to dump food availability. They spent almost half of their total foraging time on dump foods. Home range size and daily travel length were significantly decreased compared to wild foraging baboons. Baboons showed more behavioural anxiety when they were in the dump compared to their natural habitat, presumably driven by the concentrated and desirable nature of dump resources and consequently increased intragroup feeding competition. The results also showed that the thyroid and glucocorticoid hormone levels, which measure baboons’ energetic physiology, varied with food availability. Thyroid hormone levels, which are an index of basal metabolic rate, were positively related to food availability, and negatively related to distance travelled suggesting similar relationships with energy acquisition and energy expenditure, respectively. Unexpectedly, glucocorticoid levels, or physiological stress levels, were positively related to natural but not dump food availability and only related to psychosocial stress in females. Persecution events increased both behavioural anxiety and physiological stress levels in the baboons, with some evidence of a cumulative effect of two fatal shooting incidents occurring in relatively quick succession, and a faster recovery in terms of behavioural anxiety than physiological stress.
Significant differences in activity budgets and ranging patterns for the Alldays Dump Group compared to other baboon populations suggest that dump feeding might be an extreme form of anthropogenic feeding, in terms of positive energetic benefits and limited negative impacts. However, there were some significant costs in terms of physical injury and death associated with living close to the human population surrounding the dump resources, emphasising that there are always trade-offs between the benefits and risks of living in human-modified habitats.