Contextual Factors Associated with Fecal Glucocorticoid Metabolites in Juvenile Polar Bears (Ursus maritimus) and a Cohabitating Juvenile Grizzly Bear (Ursus arctos horribilis) at the Detroit Zoo

Fecal glucocorticoid metabolites have been used to evaluate responses to stressors in captive adult polar (Ursus maritimus) and grizzly (Ursus arctos horribilis) bears. However, there is a lack of physiological information on juvenile bears in captivity that could help expand the current understanding of their development and welfare. To address these questions, we tracked fecal glucocorticoid metabolites (FGMs) and behavior for 15 months in two polar bear cubs born at the Detroit Zoo, one who was mother-reared (Astra) and one who was hand-reared (Laerke), and one rescued grizzly bear cub (Jeb) reared at the Zoo. To allow access to a social partner during key developmental stages, Laerke and Jeb were housed together for eight months. Daily opportunistic samples were analyzed for fecal cortisol metabolites using an enzyme immunoassay and compared against behavior, social proximity, and environmental data gathered from 15 min focal observations. Based on a combination of generalized linear mixed models and Wilcoxon and Kruskal–Wallis tests, we found no significant variation in mean FGMs between Astra and Laerke, but both had significantly different mean FGMs compared to Jeb. We found that Laerke had higher FGM concentrations when she spent more time engaged in all-occurrence social negative behaviors and lower FGMs when engaged in social positive behaviors. For Jeb, FGMs were lower when in social proximity and higher following separation from Laerke. These data provide novel insights into the physiological states of juvenile bears during key stages and contribute to the growing body of information on polar and grizzly bear development.