More than 500 animal species haven’t been seen in 50 years, but they’re not officially extinct yet

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Biodiversity is under serious threat in many parts of the world, with more than a million species threatened with extinction, according to the UN, and projections look even worse. However, declarations of species extinction are still very rare, largely due to uncertainties about whether the last individual of a species is actually dead.

The Eskimo curlew, one of the “lost” species. Image credit Wikipedia Commons.

This has led to the growth of a group of ‘lost’ species that have not been seen for decades or even centuries, but are not declared extinct – possessing an uncertain conservation status. Now, a new study by researchers at Simon Fraser University has estimated that there are more than 500 species considered lost, which no one has seen in over 50 years.

Arne Mooers and his team scoured information on more than 32,000 species on the International Union for Conservation of Nature’s Red List of Threatened Species (known as the IUCN Red List). The IUCN defines extinct as “”when there is no reasonable doubt that the last individual of a species is dead”, which researchers say can be difficult to identify.

“We actually found there were over 500 animals living on earth that hadn’t been seen in over 50 years,” Mooers said in an interview with The Canadian Press. “That’s almost twice as many as have been declared extinct since 1500 AD. There’s a huge pool of species that we don’t know if they’re still around or not.

Species at Risk

In total, researchers have identified 562 extinct species worldwide. Amphibians topped the list with 137 species lost, followed by reptiles (257), mammals (130) and birds (38). Of these, 13% (75 species) are listed as “probably extinct” by the IUCN. The criterion the team used to list a species as lost was the missing or last seen date.

More than 90% of species are native to tropical countries, with distributions particularly concentrated in “mega-diverse” countries. Indonesia (69 species), Mexico (33 species) and Brazil (29 species) had the most lost species overall. These three countries have seen an increasing expansion of agriculture and cattle breeding in recent years.

“The fact that most of these lost species are found in tropical megadiverse countries is concerning, given that these countries are expected to experience the highest number of extinctions,” study author Tom Martin said in a statement. “While theoretical estimates of ongoing ‘extinction rates’ are good and good, looking carefully for actual species seems better.”

For researchers, this large number of “lost species” creates uncertainty about conservation prioritization efforts and our understanding of extinction rates. They suggest adjusting the IUCN RED List to allow better tracking of lost species, as well as focusing future survey efforts on identified hotspots where the existence of many species is in question.

There are about one million animal and plant species at risk of extinction, many within decades, more than at any time in human history, according to a 2019 study. The abundance of native species in the most terrestrial habitats have declined by 20% since 1990. More than 40% of amphibian species are also believed to be threatened.

The study was published in the journal Animal Conservation.

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