Seasonal food changes and feeding behaviour adaptations of savanna chimpanzees at Nguye in Ugalla, Tanzania.

We studied the feeding strategies of savanna chimpanzees (Pan troglodytes) at Nguye in Ugalla, Western Tanzania (05°13'S, 30°28'E). Among the driest most open chimpanzee habitats, Ugalla is covered mainly by woodlands. We analysed undigested contents in chimpanzee faeces, and conducted a vegetation survey and a 1-year phenology survey every 2 weeks. The fruits of some trees with the highest biomass had high appearance rates in faeces (e.g. Parinari curatellifolia and Diplorhynchus condylocarpon). Herbaceous Aframomum mala fruits grew in large patches in savanna woodland near forest edges along rivers and had the highest appearance frequency over the longest seasonal period in faeces. Other species with higher appearance rates in faeces for long seasonal periods included Grewia mollis at the forest edge and Thespesia garckeana growing on termite mounds at the forest edge. These two tree species had low biomass. Thus, savanna chimpanzees fed on some tree foods with higher biomass, herbaceous fruits instead of scarcer tree fruits, and fruits at forest edges and in forests which occupy a small portion of the study area, in addition to woodlands which occupy a large proportion. The forest edge and interior run continuously for long distances along rivers. Forest occupies 2% of this area, but chimpanzees can continuously obtain food by moving along riverine forest. To compensate for fruit scarcity in the non-fruiting (early rainy) season, chimpanzees ate fibrous, low-quality plant parts. Chimpanzees formed smaller parties when ripe fruits and unripe legumes were scarcer. Using these feeding strategies, chimpanzees adapted to savanna woodlands.