Extinct in the Wild

The Red List of Threatened Species, compiled by the International Union for Conservation of Nature (IUCN), is widely recognised as the most comprehensive, objective global approach for evaluating the conservation status of animal and plant species. Each species assessed is assigned to one of eight different categories, based on a series of quantitative criteria. Species classified as Vulnerable, Endangered and Critically Endangered are regarded as threatened; Extinct in the Wild means that these species are known only to survive in human care.

There were 68 species that underwent an improvement in conservation status according to a recent assessment of the status of the world's vertebrates on the IUCN Red List [1], all but four due to conservation measures. For these 64 species, conservation breeding was implemented as a major or minor conservation action that led to an improvement during the period of change in 16 and three species, respectively. Therefore, according to Hoffmann et al. [1], 19 of the 64 species showing genuine improvement in IUCN Red List status due to conservation measures benefitted from conservation breeding.

These figures were subsequently contested [2] and updated [3]: there were 13 instead of 16 species identified for which conservation breeding was implemented as a major conservation action. According to Conde et al. [3], for at least nine of these 13 species, zoos and aquariums also provided substantial logistical, technical and/or financial support. Overall, it seems that conservation breeding in zoos and aquariums has played a role in the recovery of one-quarter of those vertebrate species whose threat status was reduced according to the IUCN Red List.

Breeding animals in human care followed by reintroducing them back into the wild was one of the most frequently cited conservation actions that led to improvements in IUCN Red List status [1]. For birds, conservation breeding and reintroduction helped prevent the extinction of six out of 16 species that would probably have gone extinct in the absence of conservation measures [4]. For mammals, conservation breeding and reintroduction were more successful in improving conservation status than other conservation actions [5] and contributed to the genuine improvement in IUCN Red List status of nine species [6].

According to the above-mentioned evaluation [1,3,6], species previously classified as Extinct in the Wild that have improved in IUCN Red List status thanks to the reintroduction of captive-bred animals include the Przewalski's horse (Equus ferus przewalskii), black-footed ferret (Mustela nigripes) and California condor (Gymnogyps californianus). Thanks to the same conservation actions, the threat status of the Arabian oryx (Oryx leucoryx), European bison (Bison bonasus) and red wolf (Canis rufus) was reduced from Extinct in the Wild already before the time period considered.

There are 33 animal species currently classified as Extinct in the Wild on the IUCN Red List. Examples include the scimitar-horned oryx (Oryx dammah), Père David's deer (Elaphurus davidianus), Guam rail (Gallirallus owstoni), Wyoming toad (Anaxyrus baxteri), Yarqon bleak (Acanthobrama telavivensis) and Socorro isopod (Thermosphaeroma thermophilum). Thirty-one of these species are actively bred in zoos, aquariums and other animal propagation facilities, which prevent their outright extinction; 17 species are managed in a studbook-based breeding programme. Zoological institutions are uniquely placed to contribute to the conservation of species that are no longer found in the wild, with reintroduction efforts using captive-bred animals already being implemented for six species classified as Extinct in the Wild.

References

[1] Hoffmann, M. et al. (2010) Science 330: 1503–1509.

[2] Balmford, A. et al. (2011) Science 332: 1149–1150.

[3] Conde, D. A. et al. (2011) Science 332: 1150–1151.

[4] Butchart, S. H. M. et al. (2006) Oryx 40: 266–278.

[5] Hayward, M. W. (2011) Biodiversity and Conservation 20: 2563–2573.

[6] Hoffmann, M. et al. (2011) Philosophical Transactions of the Royal Society B 366: 2598–2610.