Ecology and Behavior of the Bioko Island Drill (Mandrillus Leucophaeus Poensis)

Résumé du livre

Despite once ranging across Equatorial Guinea's Bioko Island, drill monkeys (Mandrillus leucophaeus poensis) are now limited by intense bushmeat market hunting to the Gran Caldera and Southern Highlands Scientific Reserve, a nominally protected area that comprises the southern third of the island (550 km2). Few studies have investigated the ecology or behavior of wild drills, and none have been performed on the endemic subspecies on Bioko Island. The objective of this dissertation was to provide a robust understanding of several fundamental aspects of the natural history of the Bioko drill. Comparison of foraging observations and fecal samples collected between montane and lowland forest habitats during the dry seasons of three consecutive years (2009-2011) revealed distinct dietary patterns within each habitat. In lowland forests, where fruits were relatively abundant, drills were primarily frugivorous, with only 10% of their fecal samples composed of non-fruit food items. In the montane forests, where fruits were scarce, their diet was primarily composed of the pith of terrestrial herbaceous vegetation. This fallback diet was also marked by significant increases in the weight and volume of fecal samples, and in the consumption of insects, leaves, and mushrooms. Analysis the gastrointestinal parasites of Bioko drills found them to be infected by at least six parasite species common to other primates. This is the first study to report the coccidian species, Cyclospora papionis, outside of olive baboons (Papio anubis) in east Africa, representing a considerable expansion of its range. Reliable estimates of drill group sizes were made during 136 encounters. Mean group size was 3.8 individuals per group (SEM = + 0.3; range = 1-20), and on average, groups contained one adult male and one female. Stable isotope analysis of hair samples collected from drills and other medium sized mammals indicated that the dietary overlap between the primate and duiker species may be high. However, there was little evidence that this potential competition was resulting in niche shifts among species. The findings of this research contrast some of the longstanding assumptions of the ecology and behavior of the drill, and provide important information for the conservation of the species.