The Appearance and Spread of Ant Fishing among the Kasekela Chimpanzees of Gombe: A Possible Case of Intercommunity Cultural Transmission.

Chimpanzees exhibit cultural variation, yet examples of successful cultural transmission between wild communities are lacking. Here we provide the first account of tool-assisted predation ("ant fishing") on Camponotus ants by the Kasekela and Mitumba communities of Gombe National Park. We then consider three hypotheses for the appearance and spread of this behavior in Kasekela: (1) changes in prey availability or other environmental factors, (2) innovation, and (3) introduction. Ant fishing was recognized as habitual in the Mitumba community by 1992, soon after their habituation began. Apart from one session in 1978, Camponotus predation (typically with tools) was documented in the Kasekela community beginning only in 1994, despite decades of prior observation. By February 2010, ant fishing was customary in Kasekela and with one exception was practiced exclusively by chimpanzees born after 1981 and immigrant females. We hypothesize that changes in insect prey availability over time and/or the characteristics of one popular ant-fishing site may have influenced the establishment of ant fishing. Though innovation cannot be completely ruled out, the circumstantial evidence suggests that a Mitumba immigrant introduced ant fishing to Kasekela. We submit that this report represents the first documented case of successful transmission of a novel cultural behavior between wild chimpanzee communities.

Prevalence of muzzle-rubbing and hand-rubbing behavior in wild chimpanzees in Mahale Mountains National Park, Tanzania.

In 1998, four chimpanzees in the Mahale Mountains National Park, Tanzania, were observed wiping their mouths with non-detached leaves or stalks of grass, or rubbing their mouths with a tree trunk or branch, especially while eating lemons. The number of mouth-wiping/rubbing individuals increased to 18 in 1999. By 2005, 29 chimpanzees were documented wiping/rubbing their muzzles in this way. Although it is difficult to determine whether the chimpanzees acquired this behavior as a result of trial and error or social learning, the fact that chimpanzees at other sites perform this behavior with detached leaves or leafy twigs much more often than with intact items suggests the possibility that cleaning with intact plant parts at Mahale spread via social learning.

Leaf-pile pulling: an unusual play pattern in wild chimpanzees.

Play in nonhuman animals has generally been viewed as being uniform among study sites. No studies have examined whether there are local variations in play. In this work we report an apparently locality-specific form of play that is basically solo locomotor play, but also has aspects of object play and social play. We describe this unusual "leaf-pile pulling" (LPL) pattern based on video footage of the chimpanzees of Mahale, Tanzania. Typically, when a party of chimpanzees moves in a procession down a slope in the dry season, a youngster will turn around and walk backward while raking many dry leaves with both hands. This activity accumulates many dry leaves while producing a lot of sound. After the player walks 1-15 m, he/she either turns around and walks forward or moves in a somersaulting fashion. The performer usually faces an individual that is immediately following him/her in the procession. The age of the performers ranges from 2 to 22 years, but 3-10 years are most typical. Compared to younger (< 8 years) individuals, older (> or = 8 years) individuals tend to cover longer distances during play, and to be more likely to play only on sloped surfaces and during travel. One of the authors (W.W.) has only seen the behavior exhibited by five different individuals on 10-15 occasions at Gombe. The behavior is exhibited less often at Gombe than at Mahale. To date, LPL has not been reported elsewhere. The absence of LPL at other sites may or may not be explained by environmental differences, such as differences in the availability of dead leaves and sloped terrain. Although the possibility that LPL is acquired by individual learning cannot be completely ruled out, the hypothesis that it is a tradition of the Mahale study group is more likely. This suggests that play may warrant more careful consideration in studies of nonhuman primate culture.