Environmental stimuli unique to zoo environments may negatively impact animal wellbeing. Despite numerous studies on captive primates, relatively few have focused on gelada monkeys (Theropithecus gelada), particularly all-male bachelor groups, which pose unique social and management challenges. To address this gap, we collected data on grooming patterns, activity budgets, enclosure use, responses to zoo visitors, and stress-related behaviors in a six-member bachelor group of geladas at the San Diego Zoo (SDZ), comparing them to both captive and wild populations. Our study revealed that the geladas segregated themselves into two distinct subgroups. Further, each individual male had one primary social partner with whom he engaged in all (or nearly all) of his affiliative behavior. Geladas spent more time on rocky substrates and less time on grassy areas than expected based on their availability. They exhibited no abnormal behaviors and were unresponsive to visitors attempting to disturb them. Their proportion of time spent feeding and grooming resembled those of wild geladas, though they were much more sedentary. We recommend future husbandry efforts focus on promoting more physical activity and complex foraging tasks, such as harvesting underground food and capturing mobile invertebrates. Overall, this study offers insights into how the behavior of geladas at SDZ compares to that of other captive and wild populations, offering insights into the exhibit design and management practices that promote quality wellbeing in captive primates.

Data Collection

B.C. collected 120 hours of behavioral data from June 2021 to January 2022. Over this period, mean temperature was 21.9°C (+3.2) and 114.05 mm of rain fell (San Diego International Airport weather station, weather.gov). Observations took place between 9:00 and 20:00 on 45 different observation days and data were collected as evenly as possible across all time intervals. Instantaneous scan samples (Altmann 1974) were conducted at 10-minute intervals to record the number of visitors present at each of the three viewing areas, the location within the enclosure and substrate occupied by each individual, and the first behavior lasting >3 seconds for all visible individuals. Behaviors were recorded as feeding, resting, moving, allogrooming, self-grooming, stress-related behaviors, and other (Table 2). A total of 4,320 scans were conducted, with at least one individual not being visible during 646 of the scans. During the first 13 hours of data collection, individuals could not yet be reliably identified; therefore, these observations were included only in analyses of individual activity budgets and grooming (Table 3). In addition to scan sampling for behavior, we used all-occurrence sampling to note any incidences of stress-related or agonistic behaviors among the geladas.

Towards the end of the study, we also decided to collect data on zoo visitor behavior, to preliminarily assess whether visitors might influence gelada behavior or activity budgets. Therefore, data on the frequency of disturbances by zoo guests were collected during a subset of 10 study hours and were categorized as either vocal (e.g., yelling, whistling) or physical (e.g., banging on glass), similar to Sherwen et al. (2015) and Birke (2002). Between each scan, visitor behavior was continuously observed from a single designated viewing area, subsequently rotating between each viewing area to ensure complete coverage. Disturbances were recorded only when visitors actively sought the geladas' attention; undirected disturbances were excluded. Each disturbance was recorded if it occurred >5 seconds apart, and gelada reactions were observed for up to 5 seconds. This study was approved by Dean Gibson, Curator of Primates at the San Diego Zoo, and conducted solely through observational methods, without any direct animal contact.