Travel Time Predicts Fecal Glucocorticoid Levels in Free-Ranging Howlers (Alouatta palliata)

Abstract

Environmental stressors impact physiology in many animal species. Accordingly, the monitoring of fecal glucocorticoid metabolites (fGCM) has been increasingly used to evaluate the physiological costs of habitat disturbance on wild animal populations, providing a powerful tool for conservation and management. Several studies have suggested that primates in forest fragments have higher fGCM levels than those in continuous forests, yet the proximate causes of fGCM variation remain to be identified. In previous studies of Mexican howlers (Alouatta palliata mexicana) in Los Tuxtlas, Mexico, we found that individuals living in a smaller and more disturbed forest fragment consumed significantly less fruit and had a significantly higher feeding effort than those living in a bigger, more conserved forest fragment. Here, we aimed to examine the effects of fruit consumption and travel time on fGCM levels in the same two groups of howlers, during three sampling sessions that differed markedly in fruit availability. We found that fGCM levels (N = 202 fecal samples) were higher in the howler group living in the smaller forest fragment and varied seasonally in both focal groups, being lowest when fruit consumption was highest. However, our results suggest that travel time is the main factor predicting fGCM levels in howlers, and that although fruit consumption may be negatively related to fGCM levels, this relationship is probably mediated by the strong effect that fruit consumption has on travel time. Our results provide important insight into the proximate causes of fGCM variation in primates in fragments and highlight the potential conservation significance of studies showing that habitat loss and transformation can lead to increases in travel time in wild primates.