Reporting findings that help shape our understanding of how tool use has evolved among primates, researchers have discovered evidence that chimpanzees, at least under some conditions, are capable of habitually fashioning and using tools to hunt mammalian prey. The work, reported by Jill Pruetz of Iowa State University and Paco Bertolani of the University of Cambridge, will appear online in the journal Current Biology on February 22nd.
Chimpanzees are well known for their ingenuity in using tools for some tasks, such as obtaining invertebrate insects from logs or pounding open hard nuts, but there had been only fleeting evidence of chimpanzees brandishing tools for bona fide hunting.
In the new work, researchers observed tool use in hunting by the Fongoli community of savanna-dwelling chimpanzees (Pan troglodytes verus) in southeastern Senegal. Chimpanzees were observed making spear-like tools in a step-wise fashion, and subsequently using them with jabbing motions in an apparent effort to obtain lesser bushbabies (Galago senegalensis) from cavities in hollow branches or tree trunks. Bushbabies are nocturnal prosimians that retire to such hidden cavities during the day.
Although there was only one successful attempt in 22 recorded instances of the chimpanzees using the spear-like tools to find and obtain prey, the researchers observed that tool-crafting and associated hunting behaviour was systematic and consistent, suggesting that it was habitual. The hunting behaviour included forceful jabbing motions into branch or trunk hollows, and chimpanzees were seen to subsequently open the hollows by breaking wood off from a distance, suggesting that the jabbing actions were intended to immobilise bushbabies, rather than rouse them from their cavities (bushbabies move quickly and might otherwise easily evade chimpanzees once roused).
Two notable aspects of the behaviour observed in the Fongoli group were that on the one hand, it is rare for chimpanzees to consume prosimian prey-in other study sites, red colobus monkeys, hunted mainly by males, are the chimps’ most common prey-and on the other hand, the tool use appeared to be primarily restricted to females and immature individuals. These two behaviour characteristics could both be related to the fact that the Fongoli community inhabits a mosaic savannah that is relatively dry, and where red colobus monkeys are absent. This habitat may promote efforts-such as the observed tool use-to obtain meat through other means. The authors point out that the females and immature chimpanzees using the spear-like tools appear to be exploiting a niche relatively ignored by males, an observation that supports a previous hypothesis that female hominids played a role in the evolution of the earliest tool technology and suggests that this technology may have included tools for hunting.