Nutrition and foraging strategies of the black howler monkey (Alouatta pigra) in Palenque National Park, Mexico.

Food resources consumed by primates vary markedly in nutritional content. As a result, foragers must develop a feeding strategy to select resources that balance energy and macronutrient intake and reduce the consumption of fiber and toxins. In this study, we collected data on dietary patterns, rates of food consumption, and weight of food items consumed and combined them with published values of the nutritional content of Neotropical foods to estimate energy and nutrient intake during a 10-month period in two groups (N=16 individuals) of black howler monkeys (Alouatta pigra) inhabiting Palenque National Park, Mexico. Although howler monkeys are generally assumed to exploit a leaf-dominated diet and be energy-limited, our results indicated that black howlers met their estimated energy requirements, consuming an average of 0.58 MJ of overall energy per metabolic body mass per day. The howlers also surpassed protein requirements by consuming an average of 8.2 g of protein per metabolic body mass per day. The amount of time they spent resting was not correlated with the amount of leaves or fruit in the diet or with overall energy intake. Therefore, despite consuming a leaf-heavy diet during some months of the year, black howlers do not appear to be energy-limited. Additionally, the howlers maintained a relatively consistent level of average daily protein energy intake regardless of diet composition, while non-protein energy intake varied in response to the amount of ripe fruits consumed. Although our use of published nutritional data introduces error, these findings suggest that black howler feeding ecology is more similar to other fruit-eating atelines than previously suspected, and several common assumptions regarding howler behavior and feeding ecology need to be reexamined.