There are currently 80 species listed as Extinct in the Wild (EW) on the IUCN red list of threatened species, ranging from the Franklin tree to the Hawaiian crow or ʻAlalā. EW species have been rescued into captivity and are therefore entirely under human care and stewardship.
Maintaining species under human care
EW species are maintained ex-situ in zoos, aquariums, botanical gardens, and other collections. For extinct in the wild plants, this can involve carefully storing viable seeds in seed banks. However other EW species, such as the Pere David’s deer at ZSL Whipsnade Zoo, involve a lot larger space requirements and viable populations must be maintained through careful breeding programs. Maintaining viable ex-situ populations of EW species can therefore be costly and logistically challenging.
Other challenges facing EW species can be from genetic threats. These can include loss of genetic diversity and high levels of inbreeding that can lead to reduced survival or reproductive success, as often only small numbers of individuals have been rescued into captivity and ex-situ populations may remain at small size due to limited capacity in breeding facilities. Further, species bred in captive environments may experience ‘adaptation to captivity’, where individuals that survive and reproduce better in a captive environment have more offspring, so that over generations the species becomes more suited to a captive environment. This can then mean that captive-bred individuals are less suitable for a life in the wild, which can impact on the success of reintroduction programs.
Recently the challenges of maintaining a species ex-situ have been too much to save the Catarina pupfish and the Polynesian snail species Partula turgida, and they have gone extinct while under human care, like the thylacine and passenger pigeon before them. These examples highlight the importance and urgency of developing strategies to recover, not merely maintain, EW species.
Threats in the species’ native range
EW species may have been extirpated from their native range due to a variety of threats such as habitat loss and degradation, over-harvesting, disease, or introduction of invasive species. If these threats still remain in the species native ranges, this can hamper recovery efforts.
An example of this can be seen in recovery planning for the sihek or Guam kingfisher. This species is endemic to Guam but was extirpated due to predation by invasive brown tree snakes. Brown tree snakes are still present in Guam and therefore reintroduction of sihek to Guam will require efforts to suppress or eradicate the snakes. Alternatively, in cases where threats such as the brown tree snake remain in a species native range, releases to sites outside the native range which are free from the threat may be considered. Conservation translocations of species outside their native range are known as ‘assisted colonisations’, and may also be considered if the environment in the species’ native range is no longer suitable due to the emergence of new threats such as from climate change.
Recovery to the wild
Despite the challenges of recovering EW species back to the wild, there have been amazing success stories. These include the ko’ko’ or Guam rail, which was down-listed from EW to critically endangered in 2019 after reintroduction to a small island off the coast of Guam, more than 30 years after it had been extirpated from Guam. Other success stories include the species of Partula snail Partula Rosea and P. varia, which have been reintroduced to French Polynesia 25 years after they were extirpated due to predation by invasive rosy wolf snails. Are there lessons we can learn from these success stories that can help with recovery of other species that are currently on the brink of extinction?
Join us on 9th March for a free online Science and Conservation Event where we will be discussing some of the challenges to recovery of different Extinct in the Wild Species, as well as exploring some of the success stories.
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