Over the last few decades, the role of zoos has transformed significantly. Previously seen as menageries whose sole purpose was to display exotic animals for public enjoyment, many have now become leading centres for education and play a decisive role in global conservation efforts. Today’s zoos generate new knowledge on species biology and reproduction, donate to conservation projects in the field, and in some cases harbour the last living individuals of species that have been driven to extinction in the wild.

Zoos also carry out captive breeding of species, known as ex situ management, with the aim to release individuals back into the wild. Establishing new populations or supplementing existing ones using captive-bred individuals can help to save species at risk of extinction. A famous example of successful ex situ management is that of Przewalski’s horse, the last surviving subspecies of wild horse. Przewalski’s horse was driven to extinction in the wild in the 1960s by a combination of pressures from hunting, competition with livestock, military activities and climate change. Thanks to the maintenance of captive bred individuals, the species has been reintroduced to Mongolia, where there are now several hundred free-ranging individuals.

Przewalski’s horses in captivity.

Despite such high-profile conservation successes, the scientific community continues to debate the contribution of ex situ management to species conservation. Success stories such as that of Przewalski’s horse are relatively rare, and critics argue that the conservation benefits of captive breeding are often overstated. There is a lack of documentation of captive breeding programmes that state conservation as their objective from the outset. As a result, there is scarcity of systematic evidence for the success of ex situ conservation programmes more widely. To fill this information gap, we set out to gather available evidence of the positive impact ex situ management has had on species conservation.

We focused our research on terrestrial vertebrates, which are arguably the most widely studied group of animals. We gathered evidence by reviewing the published scientific literature, conducting a survey of ex situ management practitioners, and reviewing species documentation on the IUCN Red List, which is the world’s most comprehensive source of information on species’ conservation status. We searched these sources for cases in which a positive conservation impact of ex situ management had been documented.

We found that ex situ management reportedly contributed to an improvement in conservation status for 18 species over a 10-year period. These species included Przewalski’s horse and the black-footed ferret, another species that was reintroduced after having become extinct in the wild. The list also included species that had not disappeared from the wild, but were at risk of doing so. For example, the survival of the Mauritius fody, a brightly coloured songbird endemic to the island of Mauritius, was severely threatened by forest clearance and introduced predators, but a successful translocation in 2005 on to the small Ile aux Aigrettes off the coast of Mauritius produced a stable population and was enough to reduce the species risk of extinction.

The most common role of ex situ management was the provision of individuals to help increase population numbers in the wild , which showed a strong link between ex situ and in situ (meaning in the wild) conservation efforts. Although it was encouraging to see this link and retrieve reports of the positive impacts of ex situ management, it became clear that the evidence for these impacts was often not well documented. Reports of the outcomes of ex situ management programmes did not necessarily make their way into the scientific literature. Although the scientific literature is not always the most accessible due to paywalls and challenging publication processes, there is currently no alternative forum for such evidence to be peer reviewed and published. We also found that the strength of the evidence (i.e. the supporting data provided) to demonstrate the impact of ex situ management was highly variable.

Left: Black-footed ferret. Right: Mauritius fody. Photo: Ysmad (Wiki Commons).

This fragmented approach to documenting and reporting conservation impact makes it challenging to quantify the positive contribution that zoos make. Captive breeding programmes are not providing the underpinning evidence to back up claims of conservation benefits. We would suggest that, as a result, zoos that are having a positive conservation impact are under-selling themselves, while leaving the door open for critics to question their contribution. Perhaps more importantly, zoos and other ex situ programs are missing out on the opportunity to share and learn from their own and each other’s experiences, which is essential for improving techniques and increasing success.

This year, 2020, has been termed a ‘super year’ for biodiversity and the environment, with a series of major international biodiversity meetings planned. This provides an opportune moment for the ex situ community to consider what they have achieved so far, and what they can contribute to the future conservation of species.

Our study suggests that more systematic monitoring and reporting of the outcomes of ex situ management programs is essential for understanding the roles that zoos can play, and crucially, for ensuring that zoos and other ex situ programs have the greatest possible positive impact on the future of biodiversity conservation.

Black-footed ferret.

The article Fragmented evidence for the contribution of ex situ management to species conservation indicates the need for better reporting is available in Oryx—The International Journal of Conservation.

Louise Mair is a post-doctoral researcher in species conservation science at Newcastle University, UK. She aims to provide the evidence and tools required to inform and deliver species conservation policy, and has a particular interest in encouraging a greater diversity of practitioners and sectors to engage with international policy.