Bioacoustics as a tool to monitor the estrus cycle in a female slow loris (Nycticebus sp.).

Evidence-based husbandry leading to increased reproductive success and strengthening of ex situ populations of slow lorises (Nycticebus spp.) living in zoos is highly important. Better fulfillment of their social needs is one of the main priorities in achieving these objectives. We performed 21-month long acoustic monitoring of a zoo-kept female slow loris (Nycticebus sp.) housed either singly or with one of two males to examine whether her estrus cycle potentially could be detected based on her vocal activity. We found a regular cycle of remarkably increased whistle production that lasted approximately 31.2 days in a nocturnal exhibit and approximately 39 days in an off-show room. The regular cycle of increased vocal activity corresponded to a previously described estrus cycle of slow lorises and was observable in the presence of both males as well as when the female was housed singly. Additionally, vaginal smears collected from the female close to the peak period of her vocal activity showed signs of proestrus and estrus. The acoustic properties of the whistles, specifically that they did not overlap with or were loud enough to exceed background noise commonly occurring in zoos, made them perfect candidates for analyses involving automatic processing of a large number of recordings. We conclude that bioacoustics represents a promising, completely noninvasive and relatively easily applicable tool that allows detection and anticipation of the estrus cycle in some females, thus improving the social management of slow lorises living in zoos.