phaidra.vetmeduni.ac.at o:5095 DOI 10.3390/ani15233384 Effect of Noise on Bornean Orangutans’ Glucocorticoid Metabolite (GCM) Levels 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. eng Soundscape Stress Orangutan Zoo 2026-05-06T08:48:20.152Z LOMv1.0 Author BEGIN:VCARD VERSION:3.0 N:Queiroz;Marina Bonde de; FN:Marina Bonde de Queiroz X-ORCID:https://orcid.org/0000-0003-0153-586X END:VCARD BEGIN:VCARD VERSION:3.0 N:Passos;Luiza Figueiredo; FN:Luiza Figueiredo Passos X-ORCID:https://orcid.org/0000-0003-4529-9950 END:VCARD BEGIN:VCARD VERSION:3.0 N:Azevedo;Cristiano Schetini de; FN:Cristiano Schetini de Azevedo X-ORCID:https://orcid.org/0000-0003-0256-9017 END:VCARD BEGIN:VCARD VERSION:3.0 N:Schork;Ivana; FN:Ivana Schork END:VCARD BEGIN:VCARD VERSION:3.0 N:Palme;Rupert; FN:Rupert Palme X-ORCID:https://orcid.org/0000-0001-9466-3662 END:VCARD BEGIN:VCARD VERSION:3.0 N:Davies;William J.; FN:William J. Davies END:VCARD BEGIN:VCARD VERSION:3.0 N:Young;Robert John; FN:Robert John Young X-ORCID:https://orcid.org/0000-0002-8407-2348 END:VCARD https://w3id.org/kim/hcrt/scheme https://w3id.org/kim/hcrt/text Textdokument Text LOMv1.0 yes https://creativecommons.org/licenses/by/4.0 application/pdf 2858913 https://phaidra.vetmeduni.ac.at/o:5095 https://phaidra.vetmeduni.ac.at/api/object/o:5095/thumbnail LOMv1.0 discipline