Taking stock: Can captive species contribute to biodiversity conservation?

Strategic collection planning is a central component of contemporary zoological institutions, yet its underlying motivations remain debated. Zoos are recognised as contributing to biodiversity conservation, although it is unclear whether individual collections reflect this role. As visitor-derived income is the primary revenue source for most zoos, collection planning may favour large, traditionally charismatic species that attract public interest, potentially creating tension between conservation objectives and financial sustainability. Previous studies have identified a bias towards non-threatened species, but these have largely relied on global threat classifications, such as the IUCN Red List, which may overlook species of regional or local conservation importance. Here, we assess the size and diversity of zoo populations across all vertebrate taxa held in UK institutions, comparing global threat status with the representation of native and locally prioritised species. Shannon Wiener diversity indices indicated that fish were the most diverse vertebrate class (H = 5.41), while amphibians were the least diverse (H = 3.72). Population sizes of globally non-threatened species were more than double those of globally threatened species. UK native and priority species accounted for 9% and 2%, respectively, of the total BIAZA collection, with both groups represented across all vertebrate taxa. Globally threatened species native to the UK were recorded only among fish and birds. Additionally, six non-native species classified as Extinct in the Wild were identified, comprising five fish species and one bird species. Although collection planning within BIAZA institutions remains biased towards globally non-threatened species and species non-native to the UK, these findings demonstrate the capacity of UK zoos to contribute to native and priority species conservation and underline the importance of maintaining comprehensive captive populations for regional management and globally shared taxonomic data.