Chimpanzees are commonly known as ripe fruit specialists (Goodall, 1968, 1986; Hladik, 1977, 1977, 1979; Nishida, 1990; Matsumoto-Oda & Hayashi, 1997; Tutin et al., 1997; Wrangham et al., 1998; Newton-Fisher, 1999; Balcomb et al., 2000; Basabose, 2002), and this dietary emphasis is thought to be a major factor influencing their fission-fusion social organization (Wrangham, 1979; Sugiyama & Koman, 1992; Wrangham, 2000; NewtonFisher et al., 2000; Mitani et al., 2002; Lehmann & Boesch, 2004). In order to maximize their utilization of ripe fruit resources, which are generally described as patchy and variable in size (e.g., Ghiglieri, 1984 ), chimpanzee subgroups or parties fluctuate in size and individual make-up in response to resources. Presence of estrous females also influences the size and composition of chimpanzee parties, and this effect has been found to equate with food availability at some sites or even to surpass it (Goodall, 1986; Sakura, 1994; Boesch, 1996; Newton-Fisher et al., 2000; Anderson et al., 2002; Mitani et al., 2002).