Diet and activity in black howler monkeys ( Alouatta pigra ) in southern Belize: does degree of frugivory influence activity level?

Abstract

This study reports on the diet and activity budgets of Central American black howling monkeys ( Alouatta pigra) at Monkey River, Belize. This is a previously unstudied population, close to the southern boundary of the species range, and it provides comparative data on A. pigra from a new study site. Both diet and activity are within the ranges reported for other A.pigra sites and for mantled howlers ( A. palliata). No age-sex differences could be discerned in either diet or activity, though monthly variation was apparent. The monkeys switch from consuming leaves 86% of the time in January to March to consuming 67% fruit in April to July. This difference was statistically significant, and provided the opportunity to compare activity levels of the monkeys over two dietary periods, one characterized primarily by folivory, the other by frugivory. Howlers are often seen as a relatively inactive species, something that is associated with a low quality, folivorous diet. However, A. pigra have been described as being as frugivorous as possible and as folivorous as necessary. Yet, despite the opportunistic consumption of large quantities of high-energy foods, A. pigra has been observed as conforming to the howler lifestyle, resting as much as 80% of the day. The data in this paper support both of these reports. Black howlers at Monkey River Belize are typically inactive, maintaining high levels of inactivity even during months characterized by frugivory, suggesting that diet is more flexible and varied than is behavior and calling into question the assumption that howler inactivity is due to the digestion of large quantities of leaves.

The Short-Term Effects of a Hurricane on the Diet and Activity of Black Howlers (Alouatta pigra) in Monkey River, Belize

“…The prehurricane diet of the population at Monkey River is consistent with that seen in other species of howlers and other populations of A. pigra that show a large degree of seasonality in their diet [Chapman, 1987;Estrada et al, 1999;Julliot, 1994;Serio-Silva, 1997;Silver, 1998;Travers, 2000;Pavelka and Knopff, 2004]. Commonly, the monkeys decrease their consumption of fruit and flowers as well as increase their consumption of leaves during times of year when fruit and flowers are not available, which is necessary because fruit is a preferred food item but is not consistently available throughout the year [Estrada et al, 1999].…”

“…The 0.25% of time observed feeding on flowers refers to flowers produced by a vine, and this is not reflected in the phenological sampling of tree species. The normal shift in the diet towards consuming a greater proportion of fruit and less leaves in the months of March and April [Pavelka and Knopff, 2004] did not occur following the hurricane because trees were not producing either of these plant parts. Table 3 lists all of the food species eaten by the monkeys during either the preor posthurricane study.…”

“…Under normal conditions, Central American black howlers are known to be capable of surviving long periods of time on leaves; however, they prefer and consume fruit when it is available [Silver, 1998;Pavelka and Knopff, 2004]. Silver [1998] described the species as being as frugivorous as possible and as folivorous as necessary.…”

Hurricanes and coastlines: The role of natural disasters in the speciation of howler monkeys

“…In our comparison with A. palliata we found that A. pigra have significantly smaller and less variable group sizes than do A. palliata. Mean group size in A. palliata is 15.37 (Glander, 1978;Estrada, 1982Estrada, , 1984Chapman, 1987;Larose, 1996;Stoner, 1996;Estrada et al, 1999;Serio-Silva et al, 1999;Solano et al, 1999;Rodriguez-Luna, 2003;Williams Guillen, 2003;Munoz et al, 2006;Asensio et al, 2007;Dunn et al, 2009;Dunn et al, 2010) and mean group size in A. pigra is 6.83 (Silver et al, 1998;Silver and Marsh, 2003;Pavelka and Knopff, 2004;Pozo-Montuy and Serio-Silva, 2006). Considering the hurricane activity that occurs in the range of A. pigra, low group size could very well represent an adaptation to living in a stochastic environment.…”

“…When examining the relationship between fruit consumption and activity patterns we found no consistent differences within or between species in how populations adjust behaviour during periods of fruit shortage. Populations of A. pigra either decreased time spent travelling (from 9.52% to 5.45%), increased time spent inactive (from 69% to 77%) or did not adjust activity patterns in response to seasonal reductions in fruit intake Silver et al, 1998;Pavelka and Knopff, 2004). While some groups of A. palliata also did not show changes in activity that correspond to fruit production, the most common response reported in the literature is an increase in either travel time (from 18.6% to 35.8% in A. palliata in Nicaragua, Williams-Guillen, 2003) or ranging distance (from 114.05 m to 502.88 m for a population in Mexico, Estrada, 1984), which is a response that has never been reported for a population of A. pigra.…”