Environmental, nutritional and social aspects of insectivory by Gombe chimpanzees

Humans and many living apes eat insects. Insectivory by humans, chimpanzees and orangutans is often sex-biased (with females consuming insects more frequently and for longer durations than males) and associated with tool-use. Extinct hominins may also have preyed upon insects, yet models of the origins of the human diet have typically emphasized meat-eating (carnivory) over other forms of faunivory.;As one of the two closest living relations to modern humans, chimpanzees (Pan troglodytes) represent useful referential models for the behavior of extinct hominins. The manufacture and use of tools to acquire insects was among the first major discoveries made by Jane Goodall in her studies of the Kasekela chimpanzees of Gombe National Park of Tanzania. However, even after fifty years of research many basic but important questions about insectivory and insect prey choice in this community remain unanswered. Over three field seasons between February 2008 and February 2010 I conducted a study of insectivory by Kasekela chimpanzees. This study included a survey of social insects across the central and northern regions of the park, nutritional assays on insect prey (and some potential insect prey) available to the Kasekela chimpanzees, observation of chimpanzee predators, and a review of the long-term behavior records. I use the results of this study to test four hypotheses regarding insectivory and insect prey choice by Kasekela chimpanzees.;I found that availability, encounter rates, and colony abundance were not important factors in Kasekela chimpanzees' choice of insect prey. Kasekela chimpanzees favor insect prey of high caloric value and with high fat and protein content, but ignore some insect prey consumed by Pan elsewhere in Africa with the potential for high caloric and nutritional yields. On a gram-for-gram basis the macronutritional content of insects consumed by Kasekela chimpanzees are comparable if not superior to meat. Socially-learned knowledge of prey and associated foraging techniques also influence prey choice. A novel form of tool-assisted insectivory (“ant-fishing”) appeared in Kasekela in 1994 and spread rapidly through the community, becoming a customary behavior by 2010. The pattern of known practitioners in Kasekela, who are almost entirely immigrant females or native individuals born after 1981, is consistent with social transmission from older to younger individuals and among juveniles and adolescents. Though an independent innovation cannot be completely ruled out, the circumstantial evidence suggests that ant-fishing was introduced by an immigrant female from the neighboring Mitumba community.;Insects are a small but important component of the diet for Kasekela chimpanzees. Further research is warranted on the use and re-use of particular termite mounds, hives, or ant colonies, the caloric and nutritional yields for different forms of insectivory, and the specific vitamin and mineral content of insect prey and other foods for this population. Based on the results of this and previous studies, I hypothesize that termites (particularly the genus Macrotermes) and honey-making bees (particularly Apis mellifera ) are the most likely insects to have been preyed upon by extinct African hominins.