An ecological basis for large group size in <i>Colobus angolensis</i> in the Nyungwe Forest, Rwanda

Abstract

Abstract Angolan black‐and‐white colobus monkeys ( Colobus angolensis , Sclater 1980) in the Nyungwe Forest Reserve, Rwanda, are anomalous compared with conspecifics and congeners elsewhere, because they form exceptionally large groups, in excess of 300 individuals, and because of their unusually high consumption of mature leaves (∼40% of annual diet). Site factors at the Nyungwe Forest in southern Rwanda are believed to contribute to the unusual socio‐ecology of the C. angolensis residing there. Foremost, the forest provides an abundance of mature leaves that are higher in nutritional quality (protein : fibre) compared with mature leaves analysed at other African sites. The combination of a cool high elevation locale, and a relatively open canopy, may contribute to the production of high quality mature leaves at ground level and in the canopy at the Nyungwe Forest. We believe that the almost unrestricted availability of acceptable foods for Nyungwe's folivorous colobines minimizes the potential for exploitation competition for food, and is a key factor in allowing them to form exceptionally large groups.