by Playfuls Staff |
22nd February 2007
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 [more] 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
behavior was systematic and consistent, suggesting that it was habitual. The
hunting behavior 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
immobilize bushbabies, rather than rouse them from their cavities (bushbabies
move quickly and might otherwise easily evade chimpanzees once roused).
Two notable aspects of the behavior 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 behavior 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.
