The chimpanzees (Pan troglodytes schweinfurthii) of Gombe National Park, Tanzania, were weighed regularly over a period of 33 yr, resulting in 1286 measurements on 31 males and 26 females aged 2-43 yr. Female growth slowed at 10 yr and that of males at 13 yr. Median adult body mass is 39 kg for males and 31.3 kg for females. Body mass varied between years. Chimpanzees were heaviest during a period of frequent banana provisioning. They were also heavier when community range size was large and population density within the range was low. Chimpanzees were heavier in the wet than in the dry season and body mass tracked rainfall in the preceding mo except for May in which mass was anomalously low. Dominance rank is significantly correlated with body mass for females but not males. High-ranking individuals tended to maintain more stable mass. Variability in body mass was greater for young and old individuals than for prime adults.
Bibliographical noteFunding Information:
We thank the numerous researchers who helped to weigh the chimpanzees over the 33 yr and authorities of the Tanzania National Parks, the Tanzania Council for Science and Technology, and the Tanzania Wildlife Research Institute for permission to conduct the study. Many organizations have funded the fieldwork, including the National Geographic Society, the W.T. Grant Foundation, the L.S.B. Leakey Foundation, the H.F. Guggenheim Foundation, and the Jane Goodall Institute. Support for analysis and preparation of this paper came from NSF grants DBS-9021946, SBR-9319909, the University of Minnesota Graduate School and College of Biological Sciences, The American Philosophical Society, The Carnegie Corporation, the Eppley Foundation, the Jane Goodall Institute, the Windibrow Foundation, Minnesota Base Camp, and Milton Harris. We thank Berne Scale, Minneapolis, for donating the Chatillon weighing scale in 1996. We thank Craig Packer for providing his compilation of the rain data from Gombe for Fig. 1, and Joann Schumacher Stankey and Nancy Martin for data archiving and data entry. Previous statistical analysis by Kinley Larntz provided the impetus for this paper. Anthony Collins, Carola Borries, and two anonymous referees gave useful comments on the manuscript.
- Body mass
- Dominance rank
- Population density
- Range size
- Seasonal changes
- Sexual dimorphism