The Influence of Leaf Consumption on Time Allocation in Black Howler Monkeys (Alouatta pigra).

The analysis of factors that determine variation in time budgets is important to understand the interactions between environment, behaviour and fitness. We tested the hypothesis that changes in the dietary patterns of black howler monkeys (Alouatta pigra) caused by a decrease in the availability of preferred foods are a main determinant of variation in time budgets. We predicted that individuals would trade off travel time for resting time (i.e., minimize energy expenditure) as the diet included more leaves. We conducted our study in the Mexican state of Campeche between 2005 and 2008, where we studied the behaviour of 28 adult males and 32 adult females belonging to 14 different groups for a total of 3,747.2 focal sampling hours. Study groups lived in forest fragments with variation in habitat quality. Individuals showed different rest:travel trade-offs in response to leaf consumption according to the quality of the forest fragments they lived in. Individuals that lived in high-quality fragments increased resting time under more folivorous regimes, whereas those living in low-quality fragments increased travel time. Our results suggest that howler monkeys living in low-quality fragments spend more time foraging to compensate for the low quality of the available resources.