Study: Some threatened species may miss out as zoos try to balance conservation efforts with competing pressures

In the largest study of its kind, researchers at Nottingham Trent University analysed more than 7,200 species across 613 zoos in 72 countries across a 30-year period.

The team compared changes in zoo animal holdings with changes in species’ conservation status, including extinction risk, international trade protections and involvement in zoo conservation breeding programmes.

Zoos and aquariums manage the fate of thousands of species worldwide, from breeding programmes which help bring animals back from the brink of extinction, to the everyday decisions about which species to house and where.

The researchers argue the study has revealed the complex and competing factors that go into zoos’ decisions on species planning and point to ways the sector could continue to sharpen its conservation impact even further.

Working with data provided by non-profit organisation Species360, the team found that species which became more threatened on the ‘IUCN Red List of Threatened Species’ or had increased trade restrictions, were generally not more likely to be held by additional zoos.

Similarly, species which became less threatened or had trade restrictions reduced were rarely phased out.

Once species were established within a zoo, zoos generally committed to sustaining the species over the long term, the study showed.

Domestic species, pet-trade reptiles, and crowd favourites such as chickens, goats, meerkats and sheep, were among the species showing the strongest increases in zoo holdings, suggesting visitor engagement, and the funding it generates for conservation work, continued to shape collection decisions alongside formal conservation criteria.

The largest predictor of growth in zoo holdings was participation in management or breeding programmes, rather than changes in animals’ conservation or protection status, despite some species in breeding programme expansion being of relatively low conservation concern.

The researchers say this underlines coordinated, community-run breeding programmes as one of the zoo sector’s most effective conservation tools, building on the sector’s track record of high-profile ex situ recovery efforts such as the California condor, black-footed ferret and Arabian oryx.

The team argues their findings make the case for more strategic and standardised species planning frameworks, to help zoos weigh conservation value alongside these other pressures more explicitly and consistently across the sector.

These approaches should strengthen, rather than replace, the judgement calls zoos already make, they say.

“We revealed a conservation gap in zoos, finding that most did not consistently increase support for species as their conservation concern increased, nor reduce support when it decreased,” said Samantha Ward, Professor of Zoo Animal Welfare and Legislation in Nottingham Trent University’s School of Animal, Rural and Environmental Sciences.

She said: “Instead, species managed through zoo breeding programmes, including popular visitor favourites, were more likely to expand.

“Challenges for zoos globally could include limited space and expertise. There is only a certain amount of space within a zoo boundary and they must balance conservation-important species with those that bring in the visitors. Additionally, some of the rarest species can be difficult to keep and knowledge of how to house them, feed them and improve breeding may be limited.”

Lead author Hannah Jenkins, who carried out the research as part of her PhD at Nottingham Trent University, said: “What struck us wasn’t a lack of commitment, it was how rarely a change in a species’ conservation status on its own seemed to move the needle. Species-planning is a genuinely complex balancing act: zoos are weighing conservation value against space, welfare, cost and visitor engagement, often without a shared, standardised framework to guide those trade-offs.

“Our hope is that this research supports the sector with practical evidence to build clearer species-planning tools, so that as conservation needs change, zoos are even better equipped to respond."

The research, which also involved NTU’s Nottingham Business School, is published in the journal Proceedings of the Royal Society B.