Seasonal Variation in the Diets of White-Faced and Bearded Sakis (Pithecia pithecia and Chiropotes satanas) in Guri Lake, Venezuela

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Variation in rainfall provides the most readily quantifiable method to interpret seasonal influences on plant production and animal response to environmental change. But the effects of rainfall on an animal’s behavior are complex, indirect, and less predictable, than the simple measurement of rainfall might convey. From the perspective of the primate consumer (or the human observer), periods of perceived stress or food shortage often correspond to periods of lower than average rainfall, but successful “response” depends on variables that may only be indirectly related to rainfall. Knowledge of an animal’s diet, morphological or physiological adaptations of the digestive tract, variability in local plant production, duration of food shortage, body weight at the onset of the season, and reproductive or general health status all might help predict the degree of stress individuals might experience during seasonal changes in the resource base. Indeed, some examples of responses to seasonality by primates are well known, including apparent detrimental direct effects (e.g. weight loss presumably due to reduced food intake: Goldizen et al, 1988; Morland 1992) as well as indirect effects (e.g. timing of weaning: Pereira, 1992; Wright and Meyers, 1992). But there are also reports of an insignificant or lack of effect of seasonality on other population and environmental variables: infant mortality (Crockett & Rudran 1987), diet and range use (Chapman 1988), diversity of resource used in the diet (Garber 1993). Even when seasonality does appear to affect feeding behavior, the expectation of the dry season as the most stressful season is not always borne out (Cords, 1993).