Predation by female chimpanzees: Toward an understanding of sex differences in meat acquisition in the last common ancestor of Pan and Homo

Abstract

Among modern foraging societies, men hunt more than women, who mostly target relatively low-quality, reliable resources (i.e., plants and shellfish). This difference has long been assumed to reflect human female reproductive constraints, particularly caring for and provisioning mates and offspring. Long-term studies of chimpanzees (Pan troglodytes) enable tests of hypotheses about the possible origins of human sex differences in hunting, prior to pair-bonding and regular provisioning. We studied two eastern chimpanzee communities (Kasekela, Mitumba) in Gombe, Tanzania and one (Kanyawara) in Kibale, Uganda. Relative to males, females had low hunting rates in all three communities, even where they encountered red colobus monkeys (the primary prey of chimpanzees) as often as males did. There was no evidence that clinging offspring hampered female hunting. Instead, consistent with the hypothesis that females should be more risk-averse than males, females at all three sites specialized in low cost prey (terrestrial/sedentary prey at Gombe; black and white colobus monkeys at Kanyawara). Female dominance rank was positively correlated with red colobus hunting probability only at Kasekela, suggesting that those in good physical condition were less sensitive to the costs of possible failure. Finally, the potential for carcass appropriation by males deterred females at Kasekela (but not Kanyawara or Mitumba) from hunting in parties containing many adult males. Although chimpanzees are not direct analogs of the last common ancestor (LCA) of Pan and Homo, these results suggest that before the emergence of social obligations regarding sharing and provisioning, constraints on hunting by LCA females did not necessarily stem from maternal care. Instead, they suggest that a risk-averse foraging strategy and the potential for losing prey to males limited female predation on vertebrates. Sex differences in hunting behavior would likely have preceded the evolution of the sexual division of labor among modern humans.

Wood and meat as complementary sources of sodium for Kanyawara chimpanzees (Pan troglodytes)

“…Sex differences in total meat consumption by Kanyawara chimpanzees are admittedly not well documented (Gilby et al, ). In other sites, however, adult males are known both to have primary access to prey and to consume more meat than females (Fahy, Richards, Riedel, Hublin, & Boesch, ; Wrangham & van Zinnicq Bergmann Riss, ).…”

“…In other sites, however, adult males are known both to have primary access to prey and to consume more meat than females (Fahy, Richards, Riedel, Hublin, & Boesch, ; Wrangham & van Zinnicq Bergmann Riss, ). In Kanyawara, adult male chimpanzees hunt much more frequently than adult females: although females averaged about 65% of the total number of adults (54) in the Kanyawara community between 1996 and 2015, female hunters accounted for only 8.8% of 261 kills (Gilby et al, ). Furthermore, females, when they did possess meat, were likely to have that meat stolen from them by adult males (Gilby et al, ).…”

“…Kibale National Park, Uganda, is a low‐sodium environment (Mahaney et al, ; ; Reynolds et al, ). Chimpanzees of the Kanyawara community in Kibale National Park have few obvious sources of sodium, since they hardly ever eat insects and hunt mammals relatively rarely (Gilby et al, ). However, they regularly consume wood, primarily from decaying trees of Neoboutonia macrocalyx (Euphorbiaceae) located in or close to swamps.…”

“…Instead, hunting maximizes each individual's odds of obtaining enough meat to fulfill demands for micronutrients, such as minerals, which occur at high concentration in meat (Eaton & Konner, ; Liebermann, ; Lukmanji et al, ; O'Malley & Power, ). In Kanyawara, as is typical of chimpanzees, males are the main hunters, and they have greater access to meat than females (Gilby et al, ; ; Gilby, Eberly, & Wrangham, ). Since this means that females obtain less sodium from meat than males do, we examine whether females compensate for their lower meat intake by consuming relatively more wood.…”

New Observations of Meat Eating and Sharing in Wild Bonobos (<b><i>Pan paniscus</i></b>) at Iyema, Lomako Forest Reserve, Democratic Republic of the Congo

“…Yet, frequent female control of carcasses and ability to thwart theft attempts from males is still a notable difference from chimpanzees where female control is rare and females often lose control of meat to males even if they make the kill [Wakefield, pers. observation; Gilby et al, 2017;Hobaiter et al 2017; but see Pruetz et al, 2015;Samuni et al, 2018b].…”