Fongoli savanna cave chimps

Studying chimpanzee behavioral diversity is so important because they do such different things in different parts of their range. The Fongoli field study by Jill Pruetz and colleagues is very important for this reason -- they are studying chimpanzees in a different ecology from any other field site.

As a consequence they are finding some very different behaviors, from the use of sharpened sticks to probe and kill bush babies, to the new announcement that these chimps use caves to keep cool:

The research into chimpanzees' possible use of caves began when Pruetz's field assistant Mboule Camara saw the apes coming from Sakoto cave, the largest cavern within the chimp's home range. The cave is more than 15 feet deep and located at the head of a shallow ravine that was formed through water runoff from a plateau.
To determine why they might use the cave, Pruetz recorded temperature data within the cave as well as at the different habitats the chimpanzees used, such as the woodlands and grasslands. She discovered that chimps most often use the stone cave as shelter during the hottest and driest times of the year, from October to May, findings detailed in an upcoming issue of the journal Primates. It is the first study to document regular cave use by chimps.

The cave use was reported along with some other interesting aspects of their behavior, at the recent Paleoanthropology Society meetings. Here is the abstract from Pruetz and Bertolani, mentioning some of their results:

Chimpanzee (Pan troglodytes verus) Behavioral Responses to Stresses Associated with Living in a Savanna-mosaic Environment: Implications for Hominin Adaptations to Open Habitats
Chimpanzees in the newly-habituated Fongoli community in southeastern Senegal show a unique suite of behavioral adaptations to stresses associated with their savanna environment. These include using caves as shelters during the dry season, soaking in pools of water during the early rainy season, and moving and foraging at night during maximum phases of the moon. Eleven adult males of this 35-member community serve as focal subjects in a long-term study of the ecology and behavior of chimpanzees in a savanna-mosaic environment. The Fongoli chimpanzee home range is predominantly woodland and grassland with small patches of gallery forest. While chimpanzees at Fongoli are species-typical in certain regards, such as including ripe fruit in the diet during all months of the year, they also adjust their behavior to the particular stresses of this dry, hot and open environment. For example, their large home range (>63 km2) is sometimes used cyclically, with the community traveling as one large party, in contrast to the typical chimpanzee fission-fusion pattern. Here, we report on Fongoli chimpanzee activity budgets and ranging behavior during dry versus wet seasons based on over 2500 hours of observational data collected from March 2005-August 2006. Combined with data on temperature in the various habitats within the savanna mosaic, results show that Fongoli chimpanzees minimize energy expenditure during the hottest months and at the hottest time of day by resting more and traveling less in addition to selectively using small patches of closed-canopy habitats, such as gallery forest. Details of how chimpanzees alter their ranging behavior on a larger scale at these times will also be examined. The stresses associated with a savanna-mosaic environment and chimpanzees' behavioral adjustments to them have important implications for our understanding of early hominin behavior in similar environments.

The large size of foraging parties was especially important -- it is a predictable consequence of more open-country activity, as a strategy to reduce predation -- but it should remind us how unlikely it would be for early hominids to have lived in small single-male groups.

These chimpanzees may well live in more open habitat than any hominid before A. afarensis, at least as far as we can tell from the paleoecology.