Ranging Behavior and Territoriality in Chimpanzees at Ngogo, Kibale National Park, Uganda.

Abstract

Chimpanzees are well known for their territorial behavior. Males defend heavily-used core areas and routinely patrol the periphery of their territories, apparently seeking signs of or contact with individuals from neighboring communities. In this research, I add to our understanding of chimpanzee territoriality via a study of an unusually large community of chimpanzees at Ngogo, Kibale National Park, Uganda. Using 19 months of observations, I estimated the sizes of the Ngogo chimpanzee territory and core area, the most heavily used portion of the territory. Different methods produced similar estimates, although subsampling data to reduce autocorrelation substantially reduced estimates calculated using nonstatistical techniques. I found that a biologically meaningful estimate of the core area represented an area about 1/3 of total territory size. Food availability and intercommunity relations are frequently hypothesized to influence territory use and size. I assessed their effects, but found little evidence that either affected the ranging patterns of the Ngogo chimpanzees. Patrolling chimpanzees cover long distances, and patrols are likely to involve energetic costs for participants. To evaluate these costs, I compared observations of travel and feeding during patrols and matched control periods. Chimpanzees covered longer distances, spent more time traveling, and spent less time feeding during patrols than during control periods. These results suggest that ecological factors may constrain the ability of chimpanzees to patrol. I also investigated factors affecting where chimpanzees patrol. Nest counts of neighboring chimpanzees did not predict patrolling locations, suggesting that chimpanzees do not respond to power imbalances between themselves and neighbors when choosing areas to patrol. Over the long but not short term, Ngogo chimpanzees patrolled more frequently in peripheral areas where they experienced more intercommunity encounters. In the most heavily patrolled areas, intercommunity encounter and patrol frequency were also positively correlated over the short-term. I found evidence that Ngogo chimpanzees defended some boundary areas of their territory more keenly than others, apparently adjusting their territorial activities in response to different neighbors in various ways. These chapters present a picture of how chimpanzee communities use and defend their territories, and contribute to our arsenal of methods for assessing ranging and territoriality.