Proximate mechanisms governing feeding behavior and selectivity in mantled howler monkeys, Alouatta palliata

This study focuses on dry season feeding behavior and dietary selectivity in a group of mantled howler monkeys (Alouatta palliata) at the study site in the Sector Santa Rosa within the Area de Conservacion de Guanacaste, Costa Rica. Data were collected during three consecutive field seasons. An in-depth examination of the group's diet demonstrated their (1) heavy use of seasonal resources, especially fruits and flowers, and asynchronously produced Ficus products and (2) lower reliance on mature leaves. Variability in resource use was observed within and between years. Much of the within-year variability is hypothesized to be due to the changing availability of preferred resources, especially those that are seasonally produced and figs. Between-year variability in the consumption of some resources is hypothesized to be related to differential plant part production by certain tree species as well as the asynchronous nature of fig production. Tree characteristics and phenological data were used to test hypotheses related to feeding tree use. Contrary to previous reports, tree size and food crop size were not related to the use of particular trees as feeding trees. In addition, while feeding trees needed to be accessible from adjacent trees, the degree to which they were contiguous with surrounding trees did not affect their use. The group demonstrated differential home range use that appeared to be related to variability in canopy height and density and the location of preferred food species. Finally, leaf consumption in three tree species was examined to determine whether the animals may have been practicing intraspecific feeding selectivity as has been reported by other researchers studying mantled howler monkeys. Hymenaea courbaril met the criteria set forth and an intensive examination was undertaken to determine if leaves from trees that were fed from differed in measures of primary and secondary chemistry from those trees that were not fed from. While no measures of primary chemistry were found to differ between used and unused trees, leaves from unused trees and/or leaf stages contained higher levels of several sesquiterpene compounds that are hypothesized to serve herbivore deterrent functions in a Hymenaea congener as well as Pinus.