Out of sight or in too deep: Effect of visual barriers and water depth on agonistic behaviour and growth in hatchling saltwater crocodiles (Crocodylus porosus)

Out of Sight, Out of Mind or Just Something in the Way? Visual Barriers Do Not Reduce Intraspecific Agonism in an All-Male Group of Nile Crocodiles (Crocodylus niloticus)

Simple Summary

The behavior of animals living in zoos and aquariums is influenced by the exhibits they live in, similar to how the behavior of animals in nature is influenced by the ecosystem they inhabit. In zoos and aquariums, changes in exhibit design can be implemented to modify the behavior of animals to ensure they are experiencing optimal welfare. Here, we evaluated if the addition of visual barriers—physical barriers placed at the surface of the water—reduce aggression amongst male Nile crocodiles living in a zoo. Both short- and long-term monitoring found that visual barriers did not reduce aggression within the group. While ineffective at reducing aggression, this study represents the first evaluation of exhibit design in relation to the behavior of a crocodilian species in a zoo or aquarium setting. As a commonly managed taxa in zoos and aquariums, it is imperative that their behavior and welfare are assessed systematically. We hope the methodologies and learnings from this study encourage future study of crocodilian behavior and welfare.

Abstract

Here, we evaluated if visual barriers could reduce intraspecific agonism in an all-male group of Nile crocodiles (Crocodylus niloticus) living in a zoo. Crocodiles were monitored for nearly 100 h, and four “hotspots” of aggression within their exhibit were identified. Within these four locations, visual barriers were placed at the surface of the water with the goal of reducing agonism by targeting sight lines associated with their species-typical minimum exposure posture, where crocodiles submerge their body but maintain facial sensory organs above the water line. Crocodile behavior was then monitored for 226 h, evaluating both short- and long-term effects of the visual barriers. In both observation periods, intraspecific agonism was unaffected by visual barriers. However, crocodiles were more likely to be on land and closer together, after the barriers were installed, showing the barriers affected nonagonistic behaviors. Monitoring of such unintended effects is significant to ensure no welfare concerns are created in any exhibit or husbandry modification attempt. Additionally, time of day and temperature were significant predictors of behavior, highlighting the importance of such factors in the analysis of reptilian behavior. While ineffective at reducing agonism, this is the first published study evaluating exhibit design and behavior of crocodilians in zoos and aquariums. The methodologies and findings here should provide useful information for future behavioral and welfare studies of this understudied taxa.