https://phaidra.vetmeduni.ac.at/o:5095 Effect of Noise on Bornean Orangutans’ Glucocorticoid Metabolite (GCM) Levels Queiroz, Marina Bonde de Marina Bonde de Queiroz 0000-0003-0153-586X Passos, Luiza Figueiredo Luiza Figueiredo Passos 0000-0003-4529-9950 Azevedo, Cristiano Schetini de Cristiano Schetini de Azevedo 0000-0003-0256-9017 Schork, Ivana Ivana Schork Palme, Rupert Rupert Palme 0000-0001-9466-3662 University of Veterinary Medicine Vienna Davies, William J. William J. Davies Young, Robert John Robert John Young 0000-0002-8407-2348 MDPI journal article open access eng Zoos are increasingly hosting out-of-hours events such as ‘Music Nights’ to increase visitation, raising potential animal welfare concerns due to anthropogenic noise pollution. This study examined the physiological stress response, measured through faecal glucocorticoid metabolite (FGCM), of Bornean orangutans (Pongo pygmaeus; n = 6) at Twycross Zoo during four consecutive weekends of live music events. Faecal samples were collected over these weekends and compared with a comprehensive 24 h acoustic analysis of the enclosure. The acoustic data indicated that the environment was dominated by noise from the ventilation system, which masked the sound from the live music. Comparisons of acoustic metrics between Event and Non-Event periods showed that LAeq, LA10, and LA90 were significantly higher during event hours or open zoo periods. In contrast, daily means did not differ. Group-averaged FGCM concentrations were higher on Event days (mean ± SE: Event = 826 ± 99 ng/g; No Event = 701 ± 44 ng/g), but comparisons for each individual showed no significant differences (Batu: t = 0.577, p = 0.596; Maliku: t = 1.475, p = 0.212; Molly: t = 0.290, p = 0.786; Kibriah: t = 0.771, p = 0.506). In contrast, FGCM concentrations increased significantly with increasing acoustic levels (LAeq) across individuals, with Batu and Maliku generally showing higher FGCM levels in response to louder days. These findings suggest that the constant background noise may have caused partial habituation. At the same time, individual variation highlights the importance of assessing physiological responses at the individual level, as relying on group-level data may overlook adverse welfare effects on sensitive individuals. Soundscape Stress Orangutan Zoo http://creativecommons.org/licenses/by/4.0/ https://phaidra.vetmeduni.ac.at/api/object/o:5095/download 10.3390/ani15233384 https://phaidra.vetmeduni.ac.at/o:605 application/pdf Animals issn:2076-2615 VoR Animals 15 23 2.73 MB 2025