Body size effects on vertical climbing among chimpanzees
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- Hunt, K.D. Int J Primatol (1994) 15: 855. doi:10.1007/BF02736072
I analyzed observations from a yearlong study of the positional behavior of Pan troglodytesat the Mahale Mountains National Park to determine whether there are detectable differences in behavior between large and small individuals. Analysis was complicated by a weak correlation between body size and social rank. To factor out rank effects, I performed two types of analyses, depending on the type of data: (1) multiple regressions or (2) comparisons of similarly ranked animals of different body size. With social rank effects accounted for, larger males fed lower in the canopy, fed on the ground more often, fed preferentially among food tree species with smaller adult heights, and climbed significantly less often than smaller males did. Contrary to expectation, large males utilized smaller weight-bearing structures than small males did. These results suggest that large males minimized climbing versus optimizing support diameters, perhaps because vertical climbing is disproportionally expensive for larger animals. The large body weight of chimpanzees compared with other primates suggests that minimizing altitude changes, and therefore vertical climbing, is an important consideration in budgeting daily energy expenditures.