Authored by Dr. Kylen N. Gartland, manager of applied animal welfare science for the Detroit Zoological Society (DZS).

Making a happy home requires an abundance of care, creativity and finesse – especially when that home is for gorillas! 

The Detroit Zoo’s Great Apes of Harambee habitat is home to three adult male gorillas, Chipua (Chip), Kong-Mbeli (Kongo) and Pendeka (Pende). You may notice something unique about this group – there are no females! Chip, Kongo and Pende are part of a bachelor group. Although gorilla family groups are generally composed of one adult male, multiple adult females and their juvenile offspring, gorillas may also form bachelor groups composed of multiple young and maturing male gorillas. These bachelor groups provide individuals with opportunities for a healthy social environment with companions with whom to form complex and lasting relationships. 

Forming a successful bachelor group is no small feat. Zoo staff and managers must consider a plethora of variables such as age, personality and family history. Although many all-male gorilla groups are formed when the individuals are juveniles, the relationships and dynamics within the group may undergo any number of changes as individuals grow and mature. The ideal management strategy for a group of 10-year-old gorillas can look very different from that for a group of 20-year-olds. What’s more, gorillas develop unique personalities and preferences, just like humans! Plans for long-term care and well-being must integrate not only group needs but individual factors as well. 

Chip, Kongo and Pende have been a cohesive social unit for more than 20 years, due in large part to the excellent care provided by the Detroit Zoological Society team! Zoo staff are always on the lookout for new information that can help us manage the complex inter-relationship between time, group-level needs and individual-level preferences that leads to a happy, healthy home. 

One way animal care staff can ensure the gorillas are living in optimal conditions is through tools such as Qualitative Behavioral Assessments (QBAs). QBAs are keeper rating tools that allow expert care staff to evaluate the well-being of a given animal based on subtle cues like movement, posture, dynamic expressions, and individualistic indicators of emotional states. Using QBAs, care staff and welfare scientists can collaboratively explore new and innovative strategies for maximizing animal well-being.  

Recent nationwide work between members of the DZS’s Center for Zoo and Aquarium Animal Welfare and Ethics (CZAAWE) and experts at other zoos accredited by the Association of Zoos and Aquariums (AZA) created opportunities to investigate overnight housing. This work suggested that groups of younger gorillas may thrive with the constant access to group members provided by social overnight housing, while groups with more mature gorillas may benefit from the space and solitude provided by individual overnight housing. Judging what is right for each individual and each group is an ever-evolving challenge, as an individual’s well-being varies over time. The gorillas at the Detroit Zoo provided a unique opportunity to investigate overnight housing, as the group has historically been managed on a rotation with three nights spent together socially and the fourth night spent solitarily. 

To make this investigation possible, CZAAWE staff members came together with mammal supervisor Melissa Thueme and other members of the primate care team to create and validate a QBA tool just for gorillas! This tool, called the Gorilla Behavioral Assessment Tool (GBAT), combined CZAAWE staff’s scientific training with the primate care team’s gorilla expertise. Using the GBAT, primate care staff conducted three months of daily evaluations of Chip, Pende and Kongo from June to August 2022. Once the primate team had collected the data, it was time for CZAAWE to step in! CZAAWE staff used statistics to analyze the data from the GBAT evaluations to look at differences between the overnight housing conditions. 

With a lot of input from the diverse supporting departments — and more than a little math — staff concluded that the gorillas generally demonstrated increased welfare from being housed separately overnight as compared to being housed socially. Individuals were more curious, less anxious and less aggressive with other gorillas! With these data in hand, the primate care team transitioned to housing the gorillas separately every night. 

The DZS is proud to invest in studies like these that support care staff in making the best possible management decisions and offer opportunities for cross-departmental collaborations. With the support of four other AZA-accredited zoos, we have set out to establish the GBAT as a reliable and useful tool for zoos across the United States and beyond! Stay tuned for more exciting updates as we continue this study.