MOVEMENTS OF VERVETS (CERCOPITHECUS-AETHIOPS) AND PATAS MONKEYS (ERYTHROCEBUS-PATAS) AS ESTIMATORS OF FOOD RESOURCE SIZE, DENSITY, AND DISTRIBUTION

The effect of food resources on behavior has been difficult to measure . Here we use animals themselves to describe ''effective'' food abunda nce and distribution by comparing, relative to where individuals stopp ed to eat, movements of (1) adult females living in a small group of v ervet monkeys (Cercopithecus aethiops) with those living in a large gr oup and (2) vervets and patas monkeys (Erythrocebus patas). Although f emales in the large vervet group travelled farther and stopped to eat more often than females in the small vervet group, these differences r esulted from foraging in Acacia drepanolobium habitat. In A. xanthophl oea habitat, females in the large group travelled less far, travelled shorter distances between foods, and stopped as often as females in th e small group. Greater foraging costs of females in larger vervet grou ps may be offset by access to home ranges of better quality. Compared to patas, vervets travelled shorter distances, moved shorter distances between food sites, stopped less often, and had longer feeding bouts, suggesting that foods of vervets are denser and larger, overall, than foods of patas. When vervets foraged in A. drepanolobium habitat, als o the habitat of patas, their foraging behavior became more like that of patas. Vervets travelled farther, stopped more often, and spent les s time at food sites in A. drepanolobium habitat than in A. xanthophlo ea habitat, suggesting that foods are smaller and less usurpable in A. drepanolobium habitat. Distance between foods, a component of food di stribution, did not increase, however. The critical variable underlyin g usurpability of foods may be food site depletion time, a temporal me asure.