Sixty years of collection planning: what species do zoos and aquariums keep?

Strategic collection planning is essential for zoos and aquariums globally. As organizations whose primary source of income may be from visitors, zoological collections may be tempted to select large, charismatic mammal species to maintain visitor interest. Zoos and aquariums aim to breed sustainable populations of species, many of which are not mammals. While zoo advertising and marketing often showcases megafauna, there is little research on the current composition of zoo collection plans or their evolution. To investigate zoo collection planning from a global perspective, we analysed the taxonomic composition of collections in theInternational Zoo Yearbook’s list of ‘Zoos and Aquariums of the World’ from 1960 until 2018. Average proportions of mammals, birds, reptiles, amphibians, fish and invertebrates were calculated for each collection per year. Analysis revealed that in terms of species prevalence, birds were best represented, making up 31·37% of the average collection. Amphibians, by contrast, made up only 2·78% of the average zoo species. Temporal analysis revealed a significant decrease in the proportion of bird species housed in collections (P < 0·001), while a significant increase was observed for fish (P = 0·001) and invertebrates (P < 0·001). Additionally, the average number of species housed in each collection has decreased by almost a third, from 329 spp in 1960 to 225 spp in 2018. This study suggests that zoos have reduced the diversity of animals that they keep, possibly in pursuit of sustainable populations of fewer species. However, zoos and aquariums should reflect on the implications of the poor representation of the amphibian taxa.