Page 196 - Demo

Chapter 8194might reduce the likelihood of infanticide, while wild orang-utan females need to navigate a more complex social environment, with multiple males that might pose a threat. Thus, while ovulation-induced vocalisations might occasionally be observed in zoo-housed females, they might be under strong negative selection in wild orang-utan populations due to increased risk of infanticide for females who produce such vocalisations.Studying mating behaviour of orang-utans in the wild is particularly challenging for multiple reasons (Durgavich et al., 2023). First, they are predominantly solitary, which means that only one individual can be observed at a time. Second, individuals often travel outside of the study area or disappear out of the view of the observers, making it difficult to follow the same individual for prolonged periods. Third, the menstrual cycle of orang-utan females is often suppressed, either because they are pregnant, lactating, or have a negative energy balance. Fourth, if a female is cycling, it is difficult to determine whether she is ovulating: there are no clear morphological indicators, and obtaining urine samples from arboreal species can be difficult. In captivity, researchers are confronted with fewer of these limitations. Thus, studies in captivity can prepare us to conduct methodical observations by describing relatively rare behaviours that may nonetheless occur in the wild.In conclusion, we described two cases of increased proceptivity during ovulation in two zoo-housed Bornean orang-utan females. Both females also produced vocalisations during their peri-ovulatory period. In the case of Eloise, she produced such vocalisations during her ovulation consistently, for multiple years. We want to emphasise that we cannot ascribe a clear function to the vocalisations, given that our report is anecdotal (Sándor & Miklósi, 2020). Nevertheless, our observations open up possibilities that the orang-utan female vocal repertoire might include vocalisations that indicate proceptivity, and might thus be more extensive than previously thought, at least in captivity. However, it remains to be established whether such vocalisations also occur in wild orangutan females.Tom Roth.indd 194 08-01-2024 10:42