Acquiring hormonal data from small, free-ranging mammals can be challenging when conventional techniques pose too much stress on animals, e.g., by trapping, handling, and bleeding. We assessed the feasibility of measuring plasma testosterone levels indirectly via fecal testosterone metabolites (Tmet) in a small, tropical mammal, the greater sac-winged bat. Saccopteryx bilineata forms stable, harem-polygynous societies, in which males defend female groups throughout the whole year. Firstly, we validated fecal Tmet measurements by performing a challenge experiment using gonadotropin releasing hormone (GnRH). Secondly, we compared Tmet concentrations of harem males and subordinate males in fecal samples collected during the mating season, expecting that fecal Tmet concentrations should be higher in harem than in subordinate males. Thirdly, we monitored fecal Tmet concentrations, courtship intensity and territoriality of harem males during and after the mating season, expecting that fecal Tmet values in conjunction with courtship intensity and territoriality drop after the estrous period of females passed. Our study shows that fecal Tmet concentrations responded to injections of GnRH in male S. bilineata. Fecal Tmet concentrations were higher in harem males than in subordinate males, suggesting that plasma testosterone values were related to either age or social status. Intensity of courtship and territoriality of harem males decreased towards the end of the mating season, but fecal Tmet concentrations remained constant. Male courtship intensity and territoriality were not related to fecal Tmet levels, either because short-term social challenges are not reflected in fecal hormone measurements owing to the propensity of fecal hormone metabolites to integrate over several hours, or because androgen levels are not strongly related to social activities in this species.
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