An Analysis of Insectivory in Cross River Gorillas (Gorilla gorilla diehli) in the Tofala Hill Wildlife Sanctuary, Cameroon

Abstract

Gorillas have a wide range of food items in their diet; fruits, leaves, shoot, roots, piths, and insects hence are considered as generalists (Caldecott & Ferris, 2005; Inskipp, 2005). There exists some wide dietary flexibility between gorilla species (western and eastern gorillas). The main focus of the study was investigating on Cross River gorilla (CRG) insectivory and its influence on habitat range suitability at the Tofala Hill Wildlife Sanctuary (THWS). This was based on the hypothesis that insectivory is a determinant to habitat suitability in Cross River gorillas. Reconnaissance survey conducted resulted to 115 gorilla signs recorded amongst which were 19 gorilla dung samples. CRG habitat was characterized by indirect signs recorded within various vegetation type, canopy cover, slope and elevation. This was in order to understand and relate habitat range and food availability. Insect food availability was assessed based on the number of insect/ant mount recorded along CRG trails. Data analysis included Kolmogorov sminorv normality test and non-parametric Spearman’s Rho correlation test to measure relationships between variables and Kruskal-Wallis test to compare groups for significant difference. Cross tabulations were accompanied with Cramers’ V-test in order to measure the level of association between 2 categorical variables most especially in cases where they were nominal. Statistical observations were discussed at the 95% Confidence Level (Alpha=0.05). Fecal analysis revealed insect foods amongst fruits (Afromomum sp., Musa sp., Marantacae sp. etc.), and leaves in THWS CRG. Results showed that insect consumption seemed to decrease with increased altitude. The weak and negative relation in number of insect parts and altitude range permits that the hypothesis of this study be accepted. Concurrently, abundance of insect parts in feces was not necessarily dependent on altitude but dependent on age, hence adopting the hypothesis that insectivory is a determinant to habitat suitability in Cross River gorillas. This study is the very first confirmation that CRGs feed on insects; Dorylus ant and Macrotermes sp. and Cubitermes sp.