<Note> Fission-Fusion in Chimpanzees: Feeding as a Proximal Mechanism at Gombe

Abstract

INTRODUCTION Fission-fusion is the species-typical and universal social organisation of Pan troglodytes, as recognised 45 years ago by the pioneering field research of such researchers as Goodall (1968), Nishida (1968) and Sugiyama (1968). In fission-fusion, the group (or community), sub-divides into temporary parties, which may further fragment or reunite, such that over the course of a day, an individual may be solitary or sociable to varying degrees (Aureli et al. 2008). The standard variable for measuring fission-fusion is party size, that is, the number of individuals in spatial association in any one period or point in time. Explanations for variation in party size are many, but the most prevalent one is feeding competition, so that the larger the party, the greater the competition. Thus, individuals seeking to reduce or avoid competition will fission, either to forage alone or with fewer companions. Following this line of argument, we hypothesise that party sizes will be lower during bouts of feeding than before or after feeding.