Effects of Patch Quality and Feeding Subgroup Size On Feeding Success in Vervet Monkeys (Cercopithecus Aethiops)

Abstract

AbstractAcacia tortilis flowers are an important food resource of vervet monkeys (Cercopithecus aethiops) in East Africa. This paper examines the effects of tortilis patch quality and feeding subgroup size on individual and group foraging success in vervet monkeys. Feeding variables examined included net caloric gain, foraging efficiency, pick rates, and foraging bout length. The data provide some evidence in support of the hypothesis -that patch quality significantly influences foraging success. Patches where flower pick rates were higher provided foraging for a greater proportion of the troop and provided more energy intake and higher foraging efficiency for individual troop members. Phenological data indicate that flower pick rates were a direct reflection of patch size and flower cover. On the other hand, data examined here provide no support for the hypothesis that feeding subgroup size adversely affects food intake or foraging efficiency within food patches. The lack of foraging costs appears to be due to adjustment of feeding parties to the size of food patches. Troop size, however, exceeded the average number of feeding sites per A. tortilis patch. As a consequence, low-ranking troop members suffered foraging costs due to exclusion from food patches. These analyses suggest that individual differences in benefits and costs of group foraging may play an important role in the history and evolution of groups.