Study highlights perilous state of ‘extinct in the wild’ species

Study highlights perilous state of ‘extinct in the wild’ species

  • A study published in the journal Science highlights that “extinct in the wild” species, those that cling on in captivity or as part of conservation efforts outside their natural habitat, are at serious risk of disappearing entirely.
  • The researchers found that 33 animals and 39 plants have no wild population remaining, and at least 15 of these animals are down to fewer than 500 individuals.
  • The researchers found that out of the 95 species classified as extinct in the wild since 1950, 11 have gone extinct since the 1990s. On the flip side, 12 of these species have been successfully reintroduced, brought back from the brink of extinction.
  • The study highlights the challenges associated with maintaining genetic diversity in captivity and the need for more support of as well as greater coordination and communication among conservation institutions.

Hundreds of thousands of European bison once grazed the grassy slopes from Spain to Ukraine — until they gradually went extinct in the wild by 1927. But when the last free-roaming individual was shot, that wasn’t the end of the story for the species. Fifty-four bison remained in captivity, and from this small group a new population was born, with several thousand bison now roaming the ranges of Europe again.

Species are classified as “extinct in the wild” when they’re known to survive only in cultivation, in captivity, or as a naturalized population far from their natural range.

“It’s a strange liminal space: disappeared from the wild, yet not entirely extinct,” write Donal Smith, a postdoctoral researcher at the Zoological Society of London, and Sarah Elizabeth Dalrymple, senior lecturer in conservation ecology at Liverpool John Moores University.

Yet for species so perilously close to full-on extinction, Smith said, they receive surprisingly little attention. Unlike endangered species, their numbers are not monitored by the IUCN, the global wildlife conservation authority that maintains the Red List of Threatened Species. Information on how many extinct-in-the-wild individuals exist and where can be hard to find.

The sihek, or the Guam kingfisher, has been extinct in the wild since 1988. This bird is part of the Sihek Recovery Programme. Image © John Ewen.

“We were increasingly aware that this group of species existed, but maybe they weren’t getting quite the attention that they required,” Smith told Mongabay. “We thought it was sort of an ignored part of conservation.”

In light of this, Smith and a group of 13 other international researchers conducted the first study to thoroughly assess the animals and plants categorized as extinct in the wild, or EW by their IUCN designation. Their findings, published in Science, confirm that at least 33 animals and 39 plants no longer have wild populations and are kept alive only in zoos, aquariums, botanical gardens, seed banks, and other institutions.

The list of EW species is an eclectic one, write Smith and Dalrymple. “It’s a diverse set that includes the manicillo, a relative of the peanut only found in Bolivia; the Tali palm originally identified from a lone specimen on the campus of Dhaka University in Bangladesh; and a number of tree snails from the remote Society Islands in the Pacific Ocean.”

After reviewing the available data on these 72 species, Smith said they have serious concerns. First, the number of remaining individuals for many species is alarmingly low. Of the 30 EW animal species for which there are sufficient data, for example, only six have populations larger than 1,500 individuals; half have fewer than 500 individuals.

Having only a handful of individuals left in a species is risky, especially if they’re all in one place. Events like catastrophes, disease, lack of commitment from institutions maintaining these populations, or just the random bad luck having a generation of offspring of all one sex could end a species, Smith said.

Reintroduction of the Partula rosea snail on Huahine island.
Reintroduction of the Partula rosea snail on Huahine island, French Polynesia. Image © Zoological Society of London.
Bromus bromoideus, a species of grass.
Bromus bromoideus, a species of grass from Belgium that is extinct in the wild. Image © Sadrine Godefroid

Then there’s also the problem of genetic diversity.

“The smaller a population becomes, the faster it loses genetic diversity and inbreeding increases, leading to a reduction in reproduction and other fitness,” Carolyn Hogg one of the study’s co-authors and senior research manager at the University of Sydney’s Australasian Wildlife Genomics Group, said in a statement. “This is problematic for the long-term survival of the species.”

A diverse set of genes makes populations more resilient and reduces the risk of all-out extinction (or EX). For example, some individuals may have genes that make them less susceptible to a disease outbreak or may allow them to tolerate conditions brought on by a sudden drought or heat wave.

Maintaining genetic diversity in captivity requires a minimum number of individuals, usually between 30 and 50. But many of the EW populations in captivity were founded by just a handful of individuals. In some of the plant cases, the cultivated population comes from just one individual.

Another troubling trend Smith and colleagues found is the lack of communication and coordination among institutions that keep EW plants and animals alive — plants in particular.

Keeping a species alive and healthy in captivity or cultivation takes tremendous work, resources, coordination and long-term commitment. Zoos and botanical gardens are doing some tremendous work in this area, but they need more support, said Smith and Brian Zimmerman, director of conservation and science for the Bristol Zoological Society and co-chair of the IUCN’s Freshwater Fish Specialist Group, who was not involved in the study.

“The European bison, once restricted to a small population under human care, is now thriving in the wild, offering an inspirational example of what pioneering conservation work can achieve.” Smith said, “but despite heroic efforts, failures are about as common as successes.”

A Red angel's trumpet flower.
A red angel’s trumpet (Brugmansia sanguine,) is a South American flowering shrub that is extinct in the wild. In some plant cases, the cultivated population comes from just one individual. Image © John Ewen.

The researchers found that out of the 95 species classified as extinct in the wild since 1950, 11 have gone extinct since the 1990s. These include the Pinta giant tortoise (Chelonoidis abingdonii), the Christmas Island whiptail skink (Emoia nativitatis), the Po‘ouli bird (Melamprosops phaeosoma), the Catarina pupfish (Megupsilon aporus), the Saint Helena olive tree (Nesiota elliptica), the Aylacostoma stigmaticum freshwater snail, and five species of snails in the genus Partula.

Smith points to the Catarina pupfish as a cautionary tale. This small freshwater fish disappeared from the wild in 1994, partly due to groundwater extraction from the native springs where it lived in northeastern Mexico. There were still some fish in captivity, but because of poor coordination and communication among their caretakers, the fish went extinct in captivity 20 years after going extinct in the wild.

“By the time people realized there was a crisis,” Smith said, “it was too late to act.”

“Conservationists, and society more widely, must do better,” Smith and Dalrymple write. “We know that outright extinction is a real threat.”

Extinction is not only a threat but a harsh reality. Scientists agree we are experiencing a mass extinction event. Previous major extinctions, like the one that wiped out the dinosaurs, were caused by catastrophes such as volcanic eruptions, depletion of oxygen, and asteroid impact. Each of these events wiped out an estimated 70-90% of life on Earth at the time.

Our current extinction crisis is caused by humans, driven by habitat destruction and fragmentation, poaching, illegal trade, overharvesting, the introduction of non-native and domesticated species into the wild, pathogens, pollution, and climate disruption.

A Socorro dove.
A Socorro dove at ZSL’s conservation zoo in London. The species is extinct in the wild but there are hopes to reintroduce the species. Image © Zoological Society of London.

Since 1900, 543 species of vertebrates have gone extinct. And those are just the ones we know of. In the past century, we have witnessed the disappearance of the ivory-billed woodpecker (Campephilus principalis), the Round Island burrowing boa (Bolyeria multocarinata), the laughing owl (Ninox albifacies), the sea mink (Neovison macrodon), and the golden toad (Incilius periglenes), to name a few.

“The idea that there’s a species that we can no longer see living and breathing and behaving … is heart-wrenching,” Zimmerman told Mongabay.

“You see old footage of things like the ivory-billed woodpeckers and passenger pigeons and think, ‘Wow, these things existed, and they aren’t here anymore. I’ll never have a chance to see them in my lifetime. My daughter will never have a chance to see them,’” Zimmerman said. “Emotionally I find that quite difficult to comprehend.”

The loss of any species “can have a ripple effect on entire ecosystems, Hogg said in a statement, “and if we don’t take urgent action, the consequences could be catastrophic.”

When it comes to extinction, the stakes are high, but there’s also hope.

European bison are one of 12 formerly extinct-in-the-wild species that have been successfully reintroduced, along with the red wolf (Canis rufus), Española giant tortoise (Chelonoidis hoodensis), Przewalski’s horse (Equus ferus przewalskii), California condor (Gymnogyps californianus), Ko’ko’ bird (Hypotaenidia owstoni), Arabian oryx (Oryx leucoryx), black-footed ferret (Mustela nigripes), tequila splitfin fish (Zoogoneticus tequila), Yarkon bream (Acanthobrama telavivensis), the Mediterranean flower Diplotaxis siettiana, and the Hawaiian tree Hibiscadelphus giffardianus, revived from the single remaining tree on the Big Island.

“I don’t think I anticipated how many species would have been returned to the wild,” Smith said about their research. “I think both those successes and the degree of activity acts as motivation.”

Scimitar-horned oryx being released in Chad.
Scimitar-horned oryx being released in Chad after becoming extinct in the wild – the result of a global collaborative breeding program. Image © Zoological Society of London.
The first scimitar-horned oryx leaving the enclosure as part of their reintroduction in Chad.
The first scimitar-horned oryx leaving the enclosure as part of their reintroduction in Chad. Image © Zoological Society of London.

Zimmerman said one of the things that stands out about this new study is that it highlights the importance of the zoo, aquarium and botanical garden communities in addressing many of the issues related to EW species.

“There’s a lot of criticism of zoos and aquariums out there,” Zimmerman said, “and some of it is justified criticism. But, I often say to my colleagues that this is where we can come into our own. This is where we actually have a real serious frontline role to play in conservation.”

Experts at the Zoological Society of London’s conservation zoos (in London and Whipsnade) are working to keep 16 of the 38 EW animal species alive, for example. Also in the U.K., the Royal Botanic Gardens, Kew, coordinates the Millennium Seed Bank, the world’s biggest and most genetically diverse seed storage facility. It holds many plants already deemed extinct in the wild, including the world’s smallest waterlily, Nymphaea thermarum, from Rwanda.

“[T]he species has been extinct in the wild since the destruction of its native habitat in 2008,” Tim Pearce, conservation partnership coordinator at the Millennium Seed Bank, told Mongabay. “However, horticulturists at Kew Gardens have been able to grow it from seed and it now lives in Kew’s living collections in London.”

“Without these dedicated organizations and their conservation efforts, we would have already lost species like scimitar-horned oryx [Oryx dammah], several Polynesian tree snails, and the yellow flowering toromiro [Sophora toromiro],” Smith said.

“Thanks to decades of tireless work saving species, we have the opportunity to reestablish more populations in the wild; it’s imperative that conservation zoos, aquariums, botanical gardens and seed banks are given the financial — and intergovernmental — support to do so.”

Banner image: Przewalski horses and foal at ZSL’s conservation zoo at Whipsnade. A previously ‘extinct in the wild’ species, it is now returned to the wild through international conservation efforts. Image © Zoological Society of London.

Liz Kimbrough is a staff writer for Mongabay. Find her on Twitter @lizkimbrough

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Smith, D., Abeli, T., Bruns, E. B., Dalrymple, S. E., Foster, J., Gilbert, T. C., … Ewen, J. G. (2023). Extinct in the wild: The precarious state of Earth’s most threatened group of species. Science379(6634), eadd2889. doi:10.1126/science.add2889

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