RESUMO
BACKGROUND: The studies on fecal steroid metabolites published with free-living primates are limited mainly by the difficulty in obtaining samples. METHODS: A radioimmunoassay was used to measure the fecal steroid concentrations in Alouatta belzebul in the National Forest of Tapirape-Aquiri in Brazil. RESULTS AND CONCLUSIONS: Androgens were significantly higher for the adult males from the Area of Influence (AI-I group) when compared to those from the Control Area (CA group) (P < 0.05). Progestin and estrogen concentrations were higher in the females from the CA group than in those from the AI-I for both the adult females and females with offspring; however, P < 0.05 was only observed in the concentrations of fecal progestins from the adult females. The physiological differences between the AI-I and CA groups suggest that the cause was a sum of factors, such as an exposure to sound waves, feeding habits, daily activity patterns, and the habituation of the animals.