Longitudinal Analysis of Variability in Fecal Glucocorticoid Metabolite Concentrations in Three Orangutans (<i>Pongo pygmaeus pygmaeus</i> and <i>Pongo pygmaeus abelii</i>) before, during, and after Transition from a Regular Habitat Environment to Temporary Housing in Indoor Holding Facilities

Considerable research has been conducted on the effects of inter-institutional transfers, but far less consideration has been given to intra-institutional transfers and extended housing in off-habitat holding. On 15 May 2018, The Oregon Zoo’s orangutans (<i>n</i> = 3) were moved from the Red Ape Reserve (RAR) to the Veterinary Medical Center (VMC) indoor holding areas and remained there until 22 December 2020, resulting in over two years of housing in a facility not specifically designed for orangutans. This study aimed to quantify potential changes in fecal glucocorticoid metabolites (fGM) typically associated with increased adrenal activity as a result of transfers, as well as potential differences in fGM concentrations associated with housing in the two different types of locations. We collected fecal samples from all orangutans during three time periods: the initial housing at RAR (RAR1), the time spent at VMC holding (VMC), and the return to RAR (RAR2). Samples were analyzed using enzyme-immunoassay (EIA) analyses and compared using two-way ANOVA tests with Games–Howell post-hoc evaluations. The results of our analyses showed the following: (1) significant differences in fGM concentrations based on location in two orangutans, with the highest fGM concentration occurring in fecal samples collected at the VMC; and (2) a lack of significant fGM peaks following multiple intra-institutional transfers for all three orangutans. Though requiring further corroboration through future studies, we speculated that pre-transfer behavior training and intensive, continued care by familiar animal care staff may have helped to mitigate the stress responses commonly associated with transfers and major changes in housing. Furthermore, this study highlights the individualistic nature of the stress response, as illustrated by the substantial variation in fGM concentrations across different housing regimens in the three orangutans.