Tree structure and sex differences in arboreality among western lowland gorillas (Gorilla gorilla gorilla) at Bai Hokou, Central African Republic

Abstract

The aim of six months of research in 1995 on the gorillas (Gorilla gorilla gorilla) at Bai Hokou, Central African Republic, was to study the effects of tree structure, relative numbers of arboreal feeding sites, and sex differences in body size on arboreal foraging. The analysis presented here also documents inter-annual variation in fruit availability and climbing by silverback gorillas by comparing the 1995 results to those from earlier research, 1990–1992. This analysis suggests that female gorillas maintain similar levels of arboreality in fruit-rich and fruit-poor seasons and years, but silverbacks may be more terrestrial when fruit is scarce or difficult to access. Trees of different shapes present different numbers of feeding sites to bigger males and smaller females. Male climbing is affected by the availability of fruit, and small trees with narrow crowns that lend easy access to fruit from the core. This study suggests that the energetics of vertical climbing and biomechanical constraints imposed by small branch feeding sites in the periphery of trees may constrain the arboreal behavior of male gorillas. Fine-tuned comparisons of food availability, tree structure, and variation in social context of behavior across habitats, will assist efforts to understand differences in ecology among populations and species of African apes.