Temporal changes in diet of Budongo Forest Chimpanzees

Abstract

Chimpanzees (Pan troglodytes) are primates well known for performing ecological roles such as dispersal. Their populations are however dwindling where they exist and this is largely attributed to food availability. Since chimpanzees are frugivores, a recorded decline in general fruiting of most trees alongside evidence of warming temperatures in Budongo Forest raised curiosity into the likely foraging adaptation strategies by the chimpanzees. The study was thus conducted in the fully habituated Sonso chimpanzee community of Budongo Forest Reserve found on the western arm of the East African rift valley in Uganda. The study aimed to assess the (a) temporal fruiting phenology changes of Budongo chimpanzee food trees. (b) temporal changes in diet, activity budget and seasonal consumption of foods by Budongo Forest chimpanzees. It was hypothesized that the chimpanzee tree fruiting pattern could have affected chimpanzee feeding behavior. The findings were thus compared to those of previous feeding ecological studies. Direct observation was used to record tree fruiting and focal sampling to collect data on chimpanzee foraging. Analysis was conducted on long term records of monitored tree fruiting phenology in 6 compartments and chimpanzee diet composition data of Budongo Forest. Chimpanzee tree fruiting mirrored the general fruiting trend with a decline over the years. The study revealed fruit to still be the dominant food type in Budongo Forest chimpanzee diet between 2015 and 2019. This corroborates earlier findings. Its intake however decreased from an average of 70% in earlier studies to a mean of 50.7%. To cope with food stress, the chimpanzees adopted the mixed strategy of foraging which entailed an altered activity budget simultaneously consisting of either increased travel to access fruit or more rest hours coupled with incorporating more filler fallbacks. The antagonistic nature between seasonality and temporal diet composition attributes the observed changes in chimpanzee diet to a confounding factor probably but most likely climate change. The study thus confirms that there have been temporal changes in the diet of Budongo Forest chimpanzees. However, further research is required to elucidate their causes.