The Thermogenic Effect of Reproductive Hormones in Female Bornean Orangutans (Pongo pygmaeus) at Bukit Merah Orang Utan Island, Perak

Basal body temperature (BBT) is commonly linked to progesterone and oestrogen concentration, two key reproductive hormones in female humans and non-human primates. Retrospectively, little attention has been given to investigating the association between basal body temperature and reproductive hormones via non-invasive methods among orangutans. Hence, this study was carried out to identify the associations between basal body temperature and reproductive hormones via a non-invasive approach among four female orangutans at Bukit Merah. The basal body temperature of two adult females, Baboon (age 33) and Careena (age 15) and two adolescent female orangutans, April (age 13) and Kate (age 9), was measured using an infrared thermometer gun. A total of 101 faecal samples were gathered and analysed via enzyme-linked immunosorbent assay (EIA). A Spearman’s correlation coefficient test revealed a significant moderate positive relationship between progesterone and basal body temperature with r[101]=0.437, p=0.041. Nevertheless, there was no significant relationship between basal body temperature and oestradiol. These findings align with previous research conducted on other mammals, which has shown that progesterone elevation is associated with increased body heat. This result also demonstrated the reliability of using non-invasive techniques, such as infrared thermography and faecal hormone analysis, for tracking reproductive hormone changes in orangutans. This study contributes valuable data to understand the physiological effects of progesterone on thermoregulation in female orangutans and offers practical insights for captive breeding programs aimed at enhancing orangutan welfare. Future research could explore the broader implications of progesterone’s thermogenic effects on behaviour and reproductive success.