Understanding animal introductions and welfare in zoos: A scoping review

Abstract

Managing captive zoo species often requires modifying their social groups, but these changes can increase stress and aggression. Specifically, introductions of new animals to existing exhibits with established animals is commonplace, yet little has been published to systematically evaluate this process. This review used the PRISMA framework to evaluate published research on introductions of unfamiliar individuals in zoos, aquariums, and sanctuaries. Peer-reviewed studies from PubMed, Web of Science, and Scopus were screened and extracted using Covidence software. Studies were included if they provided quantitative data and before-and-after comparisons. Of 25 studies meeting criteria, most focused on primates, especially western lowland gorillas, followed by Asian and African elephants. Measured outcomes included activity levels, stereotypic behaviours, and social interactions. Although introductions often had positive welfare effects, negative impacts were also common. The most frequent introduction types were single-to-multiple and multiple-to-multiple, with evidence suggesting that multiple-to-multiple introductions may help mitigate negative welfare effects. This review emphasizes the need for more systematic introduction protocols and species-specific considerations to minimize welfare risks. Future studies should include diverse species and physiological indicators for a more comprehensive understanding of introduction effects on zoo animal welfare.