A species is considered “extinct in the wild” (EW) if it only exists under human care as an ex-situ population or survives outside its historical range as a naturalized population. Ex-situ conservation plays an important role in species protection, especially for endangered species where the natural habitat is destroyed or exposed to direct threats. Despite the efforts of zoos and botanical gardens to preserve endangered species, restoring their wild status is not always successful.
The conservation of biodiversity aims to preserve the ecological function and prevent ecological extinction. However, the release of ex-situ populations is often a lengthy process that requires careful planning, research and monitoring to ensure that the released animals or plants survive in their new habitat. The habitat into which the populations are released may differ from their natural habitat, for example. Changes in the environment such as habitat destruction, climate change or the introduction of invasive species can impair the viability of the released populations.
The Socorro dove, also known as Grayson’s dove, was exclusively native to the volcanic island of Socorro in the eastern Pacific, in the southwest of North America. It was last documented in the wild in 1972, after Socorro was used for military purposes from the 1950s onwards. The construction of facilities and the military presence led to the destruction of its habitat and the introduction of cats and rats, which ate both the chicks and the eggs of the trusting Socorro dove. Despite its extinction in the wild, there are some targeted breeding programs in human care that are trying to preserve this species and possibly reintroduce it into its natural habitat.
(Photo: © Johann Alexi, CC BY-SA 4.0, via Wikimedia Commons)
The Bali starling or Bali Mynah lived only in a 50-kilometer-long coastal strip on the island of Bali at the time of its discovery in 1910. The wild population has been almost extinct since at least 1994. During a review in 2015, it was found that fewer than 15 birds were flying in the wild, indicating the strong influence of the illegal wildlife trade. Other threats include habitat deforestation, invasive species and illegal hunting. The Begawan Foundation has been running a breeding program since 1999 and released a total of 64 Bali starlings on Nusa Penida in 2006 and 2007. Monitoring programs show that the population had increased to over 100 individuals by 2009, but it is still severely affected by illegal activities.
(Photo: © Doreen Fräßdorf, photographed at the Natural History Museum in Tring, England, 2024)
The Yangtze sturgeon is endemic to China, in the Yangtze River and its tributaries. It was last sighted in the 1990s. Changes to the habitat caused by the construction of dams have severely impacted the natural habitat of the fish species. In addition, the Yangtze sturgeon was heavily overfished, both for its fish eggs (caviar) and for its meat. Water pollution in the Yangtze River has also contributed to its decline. Several Chinese aquaculture research institutes have started breeding Yangtze sturgeon in human care. They are focusing on preserving genetic diversity and understanding the reproduction of this species in order to develop successful breeding methods.
(Photo: © Josephe Huët, Public domain, via Wikimedia Commons)
The Hawaiian crow, originally native to the upland forests of Hawaii, was last documented in the wild in 2002. The main causes of its extinction are habitat loss, diseases such as the West Nile virus and the introduction of invasive species that affect its food sources and reproduction. There have been several reintroduction attempts to reintroduce the Hawaiian crow into the wild. The first attempts, in the late 1990s with the release of offspring, were unsuccessful. Most of the birds did not survive long in the wild. There are currently efforts to save the Hawaiian crow through targeted breeding programs and monitoring strategies. In December 2024, a new attempt was launched to resettle the species on the island of Maui.
(Photo: © U.S. Fish and Wildlife Service, Public domain, via Wikimedia Commons)
The Northern white rhinoceros is considered extinct in the wild in Africa, as the last individuals were sighted in the 2000s. The species was still relatively common in the 1970s, but experienced a sharp decline due to poaching and habitat loss. They were mainly hunted for their horns, which are traded at high prices on the black market. In 2018, the last known Northern white rhinoceros was placed under protection. Currently, there are still two living female specimens in Kenya that rely on artificial insemination to ensure the survival of the species.
(Photo: © Make it Kenya/Stuart Price, Public domain, via Wikimedia Commons)
The Tequila splitfin, only discovered in 1990, has been considered extinct in the wild since 2003, mainly due to habitat loss, water pollution and invasive species such as guppies and platys. Prior to this decline, it had been successfully bred in human care, particularly at Chester Zoo. In 2014, reintroduction attempts began, with 40 males and 40 females being kept in artificial ponds. By 2021, the population had grown to around 10,000 individuals, 1,500 of which were released into the Río Teuchitlán in Mexico. The IUCN downgraded the species from “critically endangered” to “endangered” in 2018, but the population remains vulnerable to threats that could jeopardize its survival.
(Photo: © Cedricguppy – Loury Cédric, CC BY-SA 4.0, via Wikimedia Commons)
Some species that are extinct in the wild are not uncommon, such as the species of the plant genus Brugmansia (angel’s trumpet), which has been cultivated worldwide, but no longer occurs in the wild. The red-tailed black shark (Epalzeorhynchos bicolor) is also a popular ornamental fish and can be found in countless aquariums worldwide, although it was long considered extinct in the wild in its original home, Thailand. According to more recent information, some specimens of the species are said to live again in the Chao Phraya River.
About the author: Doreen Fräßdorf
Doreen Fräßdorf is the author and publisher of artensterben.de. She researches and writes about extinct and endangered species in the modern era, with a focus on red lists, scientific studies, historical sources, and current conservation efforts. The goal is a clear, evidence-based overview of biodiversity loss and species protection.
She is also the author of a non-fiction book about extinct modern-era mammals.
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