Terrestrial predator alarm vocalizations are a valid monitor of stress in captive brown capuchins (Cebus apella)

The vocal behavior of captive animals is increasingly exploited as an index of well-being. Here we show that the terrestrial predator alarm (TPA) voca lization, a robust and acoustically distinctive anti-predation vocal respon se present in many mammal and bird species, offers useful information on th e relative well-being and stress levels of captive animals. In a 16-week ex periment evaluating the effects of varying levels of physical environmental enrichment (control < toys < foraging box < foraging box and toys) in the cages of eight singly housed adult male brown capuchins, we quantified the 1) emission rate of TPAs, 2) proportions of normal and abnormal behavior sa mple intervals, and 3) fecal and plasma cortisol levels. Variation in TPA e mission across the experimental conditions was significant. We found signif icant reductions in the mean TPA production rate by the group in the enrich ed (toys, foraging box, and foraging box and toys) compared to the control condition; pre- and post-experimental conditions, however, did not differ f rom the control condition. Mean TPA production by the group was also signif icantly positively correlated to mean group levels of fecal cortisol and pr oportion of abnormal behavior sample intervals, and significantly negativel y correlated to the average proportion of normal behavior sample intervals in the group. Based on group means, plasma cortisol levels were positively, but not significantly, related to increasing TPA rate. At the level of the responses of an individual subject, however, the covariation between the v ocal and non-vocal behavioral measures and the cortisol assays seldom attai ned significance. Nevertheless, the direction of the relationships among th ese parameters within individual subjects typically mirrored those correlat ions based on group means. At both the group mean and individual levels, ou r results are consistent with the interpretation that in conditions of low environmental enrichment the study subjects were more stressed, and therefo re more reactive to the presence of a threatening terrestrial stimulus (hum an observer), than when in more enriched conditions. We suggest that protoc ols to evaluate the effectiveness of enrichment for captive species other t han brown capuchins could also profitably exploit TPAs as a first-line moni tor or as corroboratory evidence of current well-being. Zoo Biol 18:295-312 , 1999. (C) 1999 Wiley-Liss, Inc.