Researchers working in West Africa have observed male chimpanzees taking great risks in order to obtain cultivated fruit, which they then exchange with females, who often became more willing to mate as a consequence.
Kimberly Hockings, of the University of Stirling in Scotland, and her colleagues have spent the last two years observing the behaviour of a small community of chimps in part of the Republic of Guinea called Bossou.
Although the chimps were rarely observed exchanging wild plant foods, they were seen to exchange fruits grown by humans far more frequently. The behaviour therefore constitutes a unique adaptation to life in a human-influenced environment. It is also the first known example of of the sharing of food amongst chimps that are not related to each other.
During the course of the study, it was found that adult male chimps far more likely than juveniles or females to raid the crops. Males were frequently observed climbing trees located in highly exposed crop fields next to villages in order to obtain the papaya grown by humans.
The farmers would often try beating the crop-raiding chimps away with sticks. And, before embarking on their raids, the males often scratched themselves roughly, an indicator of anxiety. It seem would seem that they knew that what they were about to do was risky.
The males appear to raid the crops in order to impress females. Although the raids took place whether or not females were present, the daring males always transported the stolen fruits to forested areas. 90% of the time, they would then share the fruits with females of a reproductive age. And those males that shared the most fruit mated with, and were groomed by, females more often than others.
It is unclear whether this behaviour is widespread among chimpanzees. Recent research suggests that learnt behaviours can be transmitted within and between groups of chimps, so crop-raiding could be a “custom” that is unique to the group observed in this study.
Hockings, K. J., et al. (2007). Chimpanzees share forbidden fruit. PLoS One 2 (9): e886. doi:10.1371/journal.pone.0000886. [Full text]