Page 193 - Demo

Proceptive vocalisations in orang-utan females1918DiscussionIn this anecdotal report, we describe two cases of ovulation-induced proceptivity and vocalisation in zoo-housed Bornean orang-utans. First, we described the case of Temmy, who was likely ovulating when we opportunistically played long call recordings to her. She showed a strong bodily and vocal response to these calls, but her response disappeared after two days. A follow-up experiment suggests that her change in response did not seem to be driven by habituation. Second, we described the case of Eloise, a female who consistently produced specific vocalisations during ovulation, paired with increased proceptivity towards the male she was housed with. When she reached post-reproductive age, she ceased producing this vocalisation. Even though we want to emphasize that anecdotal reports should be interpreted with caution (Sándor & Miklósi, 2020), our report suggests that changes in orang-utan female’s behaviour and vocal repertoire might reflect proceptivity during ovulation. Below, we discuss possible implications for our understanding of the role of female orang-utan behaviour in facilitating mating in captivity and in the wild.As mentioned in the introduction, previous studies have described that orangutan females show changes in proceptivity across their menstrual cycle. Our results further substantiate this pattern. We observed how Temmy responded very strongly to male long calls during her ovulation. She actively approached the source of the sound, while she did not do this during control trials. Furthermore, this behaviour was not observed outside of her peri-ovulatory period. Her behavioural response seems to suggest male-seeking behaviour, which would be especially relevant for a semi-solitary species like Bornean orang-utans. Such ovulation-dependent male-seeking behaviour has previously been described in other mammal species (rats, Rattus norvegicus: Nofrey et al., 2008; sheep, Ovis ammon: Sutton & Alexander, 2019). More specifically, in some primate species females actively seek proximity with males during ovulation (reviewed in Dixson, 2012). Our observations of Temmy suggest male long calls might induce maleseeking behaviour in ovulating orang-utan females, which could results in proximity with preferred flanged males. Some studies on wild orang-utans provide indirect evidence for this: Sumatran orang-utan females seem to approach long calls irrespective of their reproductive state (Mitra Setia & van Schaik, 2007), while in Bornean orang-utans only sexually active females without dependent infants approached long calls (Spillmann et al., 2010). However, these studies did not Tom Roth.indd 191 08-01-2024 10:42