Chimps found using spears
Feb 23,2007 00:00 by Bend Weekly News Sources

Chimps in Sen­e­gal are reg­u­lar­ly mak­ing and us­ing spears to hunt oth­er, small pri­ma­tes, with­out hu­man help, ac­cord­ing to re­search led by an an­thro­po­l­o­gist. 

It’s the first study to re­port reg­u­lar tool use by non-hu­mans while hunt­ing oth­er ver­te­brates, ac­cord­ing to the U.S. Na­tion­al Ge­o­graph­ic So­ci­e­ty, which helped fund the work.

A bush­ba­by (Otole­mur gar­netti) was a re­ported vic­tim of a spear-wielding chimp. (Im­age cour­te­sy U.S. Nat'l Hu­man Ge­nome Inst.)

Anthropologist Jill Pruetz of Io­wa State Uni­ver­si­ty in Ames, Io­wa, and Pa­co Ber­to­la­ni, a grad­u­ate stu­dent at the Uni­ver­si­ty of Cam­bridge, U.K., doc­u­mented 22 cases of chimps mak­ing spears to use in hunt­ing down smaller pri­ma­tes in cav­i­ties of hol­low branches or tree trunks.

Chimps made the spears of live bran­ches that they trimmed, then sharp­ened with their teeth, Pru­etz and Ber­to­la­ni said. They found the act­i­vi­ties at Fon­goli, Sen­e­gal, in 2005 and 2006. 

A pa­per on the find­ings is to ap­pear in the March 6 is­sue of the re­search jour­nal Cur­rent Bi­ol­o­gy. The pa­per was
on­line in the jour­nal start­ing to­day.

“We came up­on the dis­cov­ery quite un­ex­pect­ed­ly,” said Pruetz. 

“There were hints that this be­hav­ior might oc­cur, but it was one time at a dif­fer­ent site. Then I talked to [Bertolani] and he told me that he saw a fe­male hunt with tools. When he looked through orig­i­nal da­ta... we real­ized he had oth­er ev­i­dence and ob­ser­va­tions of them prob­a­bly do­ing the same thing. While in Sen­e­gal for the spring se­mes­ter, I saw about 13 dif­fer­ent hunt­ing bouts. So it real­ly is ha­bit­u­al.”

Chimps repeatedly jabbed tools in­to hol­low trunks or branches and smelled and/or licked them up­on ex­trac­tion, the re­search­ers said. Two of the 22 cases were judged as mere­ly play­ful—in the case of an in­fant male—or ex­plor­a­to­ry. In all oth­er cases, the sci­ent­ists said the chimps poked with such force that prey could have been in­jured. They de­s­cribed just one case in which a chimp ex­tracted a bush­ba­by, a smal­ler pri­mate, us­ing a spear.

Al­though hunt­ing is pre­dom­i­nantly an adult male ac­tiv­i­ty with chimps, on­ly one adult male of 11 ma­les in the chimp com­mu­ni­ty was seen in the tool-assisted hunt­ing, the in­ves­ti­ga­tors said. The rest were ad­o­les­cent or youn­ger chimps of both sexes.

“In the chimp lit­er­a­ture, there is a lot of dis­cus­sion about hunt­ing by adult ma­les, be­cause ba­si­cal­ly, they’re the on­ly ones that do it, and they don’t use tools,” said Pruetz.

“Fema­les are rare­ly in­volved. And so this was just kind of as­tound­ing on a num­ber of dif­fer­ent lev­els. It’s not on­ly chimps hunt­ing with tools, but fe­ma­les—and the ones who hunt­ed the most with them were ad­o­les­cent fe­ma­les.

“It’s clas­sic in pri­ma­tes that when there is a new in­no­va­tion, particularly in terms of tool use, the young­er gen­er­a­tions pick it up very quick­ly. The last ones to pick up are adults, main­ly the ma­les,” she said. “This is be­cause im­ma­tures learn from the ones they are most af­fil­i­at­ed with, their moth­ers.”

The find­ings sup­port a the­o­ry that fe­ma­les might have played a role in the ev­o­lu­tion of tool tech­nol­o­gy among early hu­mans, Pruetz said. Those tech­nolo­gies would have in­clud­ed both hunt­ing- and gathering-related ac­tiv­i­ties. “The com­bi­na­tion of hunt­ing and tool use at Fon­goli, be­hav­iors long con­sid­ered hall­marks of our own spe­cies, makes the pop­u­la­tion es­pe­cial­ly in­trigu­ing,” wrote the sci­ent­ists in the Cur­rent Bio­lo­gy paper. 

“The ob­ser­va­tion that in­di­vid­u­als hunt­ing with tools in­clude fe­ma­les and im­ma­ture chim­panzees sug­gests that we should re­think tra­di­tion­al ex­pla­na­tions for the ev­o­lu­tion of such be­hav­ior in our own line­age. Learn­ing more about the unique be­hav­iors of chim­panzees in such an en­vi­ron­ment, be­fore they disap­pear, can pro­vide im­por­tant clues about the chal­lenges fac­ing our ear­li­est an­ces­tors.”

Courtesy National Geographic Society and World Science staff