2019 Volume 35 Issue 2 Pages 87-92
We studied wild chimpanzees (Pan troglodytes) in the Ugalla savanna woodland area of Tanzania from 1995 to 2012. Ugalla is the eastern-most chimpanzee habitat and is one of the driest and most open areas. From 52 direct observations of unhabituated chimpanzees, we found 59.6% of parties (temporal sub-groups in a unit-group) in trees and 32.7% on the ground; 59.6% of parties were observed in forests, 38.5% in woodlands, and none in grasslands. The mean±SD party size (excluding infants) was 3.1±2.2 (range 1.10) individuals. Party sizes were smaller in the rainy season (2.0 individuals) than in the dry season (3.6 individuals). This suggests that chimpanzees reduce feeding competition by forming smaller parties, especially in the rainy season when fruit availability is low and/or food patches are small. We found a lone male eight times, whereas we found a lone female only once. Mixed parties contained more females (1.9 individuals) than males (1.4 individuals). Mothers with infants might join a mixed party to reduce predation risk. The size of mixed parties with oestrous female(s) averaged 5.7 individuals, whereas that with no oestrous female averaged 4.0 individuals. We found four consort parties but no all-male party. This suggests that male chimpanzees in Ugalla frequently foraged with oestrous females but did not patrol their territory because their home range is huge and their population density is very low. Chimpanzees in Ugalla changed their party size and composition according to their feeding, anti-predation, and reproductive strategies to adapt to a savanna woodland area.
