Behavioral Ecology and Sociobiology

, Volume 61, Issue 11, pp 1771–1779

Risk-prone hunting by chimpanzees (Pan troglodytes schweinfurthii) increases during periods of high diet quality

Original Paper

DOI: 10.1007/s00265-007-0410-6

Cite this article as:
Gilby, I.C. & Wrangham, R.W. Behav Ecol Sociobiol (2007) 61: 1771. doi:10.1007/s00265-007-0410-6

Abstract

Most studies suggest that during times of nutritional stress, an animal faced with two foraging choices should follow a risk-prone strategy, choosing the option with highest payoff variance. This “scarcity/risk” hypothesis was developed to account for the foraging patterns of small animals with high metabolic rates susceptible to the threat of starvation. In this paper, we propose that animals should also be risk-prone when their diet quality is particularly high, far exceeding that which is needed to survive. Under these circumstances, the costs of experiencing a low or negative payoff can easily be recouped. We suggest that large-bodied omnivores are most likely to adopt this “abundance/risk” strategy. We investigate this question among wild chimpanzees (Pan troglodytes) that choose between a risk-averse strategy of feeding on plant material and a risk-prone strategy of hunting red colobus monkeys. Using 14 years of data on the Kanyawara chimpanzees of Kibale National Park, Uganda, we find strong evidence that chimpanzees follow the “abundance/risk” strategy. Both hunting rate (hunts/100 observation hours) and the probability of hunting upon encountering red colobus monkeys were positively correlated with seasonal consumption of ripe drupe fruits, a class of preferred food associated with elevated reproductive performance by females. Critically, these results remained statistically significant after controlling for the potentially confounding effects of male chimpanzee party size and the presence of sexually receptive females. These findings suggest that the relationship between risk-sensitive foraging and diet quality depends upon the daily probability of starvation, the number of alternative foraging strategies, and the degree to which diet quality satisfies an animal’s nutritional requirements.

Keywords

ChimpanzeeHuntingRisk-sensitive foragingDiet quality

Copyright information

© Springer-Verlag 2007

Authors and Affiliations

  1. 1.Department of AnthropologyHarvard UniversityCambridgeUSA