Ecology of Cross River gorillas (Gorilla gorilla diehli) on Afi Mountain, Cross River State, Nigeria

by McFarland, Kelley Lee, Ph.D., CITY UNIVERSITY OF NEW YORK, 2007, 425 pages; 3283133


This dissertation presents the first detailed descriptions of Cross River gorilla habitat, diet, ranging behavior and grouping patterns. Field work was conducted during 32 months between 1996 and 1999 on Afi Mountain in Cross River State, Nigeria. The types of data collected include: (1) habitat types and topography mapped using line transects, (2) climate, (3) temporal and spatial availability of tree and herb foods using phenological and enumeration studies and (4) gorilla diet, ranging behavior and grouping patterns assessed from indirect evidence (feeding trails, nests and feces).

The Afi gorilla diet was found to be similar to that of other western gorillas, but differed in several ways. Most notably, Afi gorillas experience a prolonged and more severe period of fruit scarcity due to the region's special climate and the absence of important fallback fruit foods that are common at other sites. This likely explains why leaves and particularly bark, were more abundant in the Afi gorilla diet compared to other western gorillas.

As predicted by their frugivorous diet, Afi gorillas had a relatively large annual home range. Ranging behavior was clearly influenced by variation in temporal and spatial availability of tree and herb food resources and predation risk (human hunting) across their home range. The study group traveled longer distances daily when consuming widely scattered and/or patchy fruit or herb food resources. The study group utilized different sectors within their range in a non-random efficient manner corresponding to variation in availability of preferred foods across sectors and avoidance of sectors with high hunting pressure.

The study group most often contained 18 nesting individuals including at least two adult males. Nest group size was highly variable between consecutive nest sites and seems to be best explained by flexible grouping behavior; alternative explanations were investigated and eliminated. The pattern of nest group size variability suggests that at times individuals of a smaller-sized group may have joined the study group, while on other occasions the study group may have divided into subgroups. Group flexibility occurred relatively frequently when gorillas consumed large amounts of fruit or preferred herbs during the period of fruit scarcity.

AdviserJohn F. Oates
Source TypeDissertation
SubjectsPhysical anthropology
Publication Number3283133

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