Long-Term Habitat Use by Mountain Gorillas (Gorilla gorilla beringei). 2. Reuse of Foraging Areas in Relation to Resource Abundance, Quality, and Depletion

Resource depression caused by current feeding and the rate of resource renewal should influence foragers' decisions about when to revisit foraging areas. Adjustment of foraging paths and revisit rates should be particularly important when resources renew slowly. Foragers can also benefit by returning more often to highly profitable than to less profitable foraging areas. Many highly frugivorous primates seem to time revisits to fruit sources so as to harvest fruit efficiently and, also, use efficient search paths. Fewer data on non-frugivores exist. Mountain gorillas are folivores that eat mostly perennially available, continuously growing herbs and vines. Vegetation regenerates slowly from the effects of gorilla trampling, though trampling can also facilitate food species productivity, at least in the short term. Adjustment of intervals between visits to foraging areas to the extent of previous use and to resource renewal rates should increase gorilla foraging efficiency. Long-term data on habitat use by 6 mountain gorilla social units show that revisit intervals vary in association with variation in the extent of previous use and in plant productivity. However, they also revisit areas more often, the higher the biomass and nutritional quality of food there. These data are generally consistent with the hypothesis that the gorillas crop resources on a sustained-yield basis, though more precise data on areal revisits and complementary long-term data on vegetation composition would be needed to test the hypothesis.