Chimps With Spears

In a comment to the last post, "Korax" mentions a paper published online in Current Biology this week on chimpanzee tool use. The tool use described in this paper is, as far as I can tell, as or more complex than any previously witnessed in chimps. Here's the abstract:

Although tool use is known to occur in species ranging from naked mole rats [1] to owls [2], chimpanzees are the most accomplished tool users. The modification and use of tools during hunting, however, is still considered to be a uniquely human trait among primates. Here, we report the first account of habitual tool use during vertebrate hunting by nonhumans. At the Fongoli site in Senegal, we observed ten different chimpanzees use tools to hunt prosimian prey in 22 bouts. This includes immature chimpanzees and females, members of age-sex classes not normally characterized by extensive hunting behavior. Chimpanzees made 26 different tools, and we were able to recover and analyze 12 of these. Tool construction entailed up to five steps, including trimming the tool tip to a point. Tools were used in the manner of a spear, rather than a probe or rousing tool. This new information on chimpanzee tool use has important implications for the evolution of tool use and construction for hunting in the earliest hominids, especially given our observations that females and immature chimpanzees exhibited this behavior more frequently than adult males.

The "prosimian prey" the chimps were hunting were lesser bushbabies like the one in the picture. Here's a more detailed description of the behavior from the paper. Keep that cute little animal in the picture in mind when you read this. Poor little things.

Chimpanzees forcibly ''jabbed'' (sensu Marlowe [16]) tools into hollow trunks or branches multiple times and smelled and/or licked them upon extraction. In only two of 22 cases was tool use playful (in the case of the infant male) or exploratory in nature (''investigatory probe'' [3]). In all other cases, chimpanzees were judged to use such force in inserting the tool that prey within the cavity could have been injured. In all observed cases,chimpanzees used one hand in a ''power grip'' [17] to jab the tool downward multiple times into the cavity. In the single instance in which a chimpanzee was observed to extract a bushbaby, it was unknown whether the prey was alive or dead after the use of the tool, but it made no attempts to escape, nor did it utter any vocalization. In that case, the chimpanzee ultimately broke off the terminal end of the hollow branch by moving several meters up the large (>10 cm diameter) branch and jumping on the branch until it broke off. She then climbed down, reached into the cavity, and pulled out the bushbaby. (p. 2)

I don't know what sorts of implications this has for theories of chimp culture. It's not clear how this behavior developed and whether it has changed over time. It is interesting that most of the instances of spear use were by adult females and young chimps, since other aspects of chimp culture seem to be passed on mostly through females, with males only showing them while young and still under their mother's care.