A photo of a gorillas eating off a branch

24-hour welfare of gorillas and drill monkeys

The Detroit Zoological Society firmly believes in promoting great welfare for the entire lifespan of animals in their care, all 24 hours of the day. Thus, it is important to ensure that the animals still experience great welfare after their caretakers and all the visitors have gone home for the night. Although this is obviously critical for nocturnal animals, even animals that are active during the day such as monkeys and apes need a good night’s sleep to be healthy and happy.

The gorillas and drill monkey at the Detroit Zoo live in a mixed-species group that, depending on the season, share a large indoor dayroom and/or outdoor yard during the day. However, the two species are separated at night and have alternating access between the indoor habitat and other night rooms. The purpose of this project was to use a combination of behavioral assessments by caretakers and endocrine measures to better understand the impacts of these alternating housing strategies on both species.

Non-invasive measurements of fecal glucocorticoid metabolites (FGMs; sometimes referred to as “stress hormones”) in the gorillas showed an interesting trend. Although hormone levels varied only slightly between nights spent in the indoor habitat compared to the night rooms, the location where the gorillas spent the day exerted a strong effect. When the gorillas had access to both the indoor and outdoor habitats during the day, they showed significantly higher levels of FGMs in the night rooms compared to the indoor habitat. This effect of night location was not evident when they spent the day in only the indoor or outdoor habitat, without the choice to move between the two spaces. Intriguingly, this trend suggests that going from the housing condition with the most options during the day was associated with a stronger reaction to occupying the most restricted space at night. However, we did not see a similar trend for the drill monkey. These results suggest that giving gorillas more choices about where they spend their time may improve their welfare.