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

Abstract

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.

A global comparison of the nutritive values of forage plants grown in contrasting environments

“…Many species of arthropods, birds and mammals actively select or avoid plants based on their nutritive values (Amato and Garber 2014; Greenberg and Bichier 2005). This dataset demonstrates that these decisions are crucial.…”

Howler monkey foraging ecology suggests convergent evolution of routine trichromacy as an adaptation for folivory

“…Dichromatic advantage for capturing cryptic invertebrates has been found and is argued to maintain the presence of dichromats in other platyrrhine species via balancing selection (Hiwatashi et al, 2010;Kawamura et al, 2012;Melin, Fedigan, Young, & Kawamura, 2010;Melin et al, 2007;Smith et al, 2012). Because trichromatic howler monkeys primarily obtain their protein from leaves (Amato & Garber, 2014), they may not experience a disadvantage of having a population solely comprised of trichromats, who should be able to locate both fruits and leaves. Even for plant species in which young leaves are greenish, the smaller leaf size and/or distinctive shape would be a visual cue accessible to both dichromats and trichromats.…”

Digestive enzymes of human and nonhuman primates

“…Recent work on primate nutritional ecology has highlighted the many challenges primates face to meet not just overall energy requirements, but also to balance micronutrients and protein intake, all while dealing with fiber, tannins, and toxins contained in foods . The ability to meet nutritional goals depends in part on foraging decisions and the nutritional composition of food items . However, it is also constrained by the gut's capability to extract these nutrients, which is where digestive enzymes and variation in them undoubtedly play a key role …”