Effects of a recurring late-night event on the behavior and welfare of a population of zoo-housed gorillas

The impact of visitors on the well-being of captive animals presents both positive and potentially negative consequences. While some amount of novelty through visitor stimulation offers the opportunity for a more complex captive environment, anecdotal evidence from primate staff observations at the Smithsonian's National Zoo and Conservation Biology Institute suggested that gorillas exhibited increased restlessness during the annual month-long late night ZooLights (ZL) event than before it. The current study compared activity budgets, aggression (interactions involving contact between conspecifics and displays toward visitors), and abnormal behaviors in two groups of socially housed gorillas for 1-month periods before, during, and after the 2015 ZL event. We also compared the fecal glucocorticoid metabolite profiles of all six gorillas across these same observation periods. Physiologically, most individuals appeared to cope appropriately with the increased visitor presence during the event. We saw little difference in contact aggression; however, abnormal behavior was observed in some gorillas during and after the event, which highlights the importance of individual analysis and data interpretation. As predicted, we found that the majority of gorillas rested less during ZL than during other observation periods, particularly adult females in the mixed sex troop. Preliminary results of this study aided the decision of zoo management to close initially the Great Ape House and subsequently most animal buildings during future ZL events to avoid the potential disruption of normal activity patterns. While the findings of this study were mixed as to the impact of the event on these gorillas, the results suggest that zoos should carefully consider the possible ramifications of keeping great ape buildings open for lengthy multi-night events.