More Than 500 Animal Species Are Considered 'Lost'

Researchers believe some of them will be found again.

Miles’ robber frog (Craugastor milesi)
Thought to be exinct, Miles' robber frog (Craugastor milesi) was rediscovered in 2008.

Tom Brown

There are more than 500 species that are “lost,” researchers say in a new study. On the upside, scientists believe that some will be found again.

An international team reviewed data on 32,802 species that were on the International Union for Conservation of Nature (IUCN) Red List, which is a database of threatened species. The researchers identified 562 that haven’t been seen in half a century but have not been declared extinct.

“We defined ‘lost’ species to be those that have not been seen in at least 50 years. That is arbitrary, of course, but it is a common threshold in conservation biology,” coauthor Arne Mooers, a biodiversity professor at Simon Fraser University in British Columbia, tells Treehugger.

“In the 1980s, 50 years without a sighting was suggested as a definition for considering something extinct. As another example, a species is considered ‘native’ in Canada if it has been here for at least 50 years.”  

In order to find the lost species, researchers just spent a lot of time looking.

“We (well, Dr. Tom Martin and an SFU undergraduate, Gareth Bennett) simply trolled through the IUCN Red List looking for candidate species using elbow grease and a bespoke computer program written by Andrew Fairbairn, and then they followed up by searching the primary literature to identify last confirmed sighting dates,” Mooers says. “And then Gareth used Google to see if any of our candidates had been rediscovered very recently (indeed, about 50 species on our list had!).”

Of the species they uncovered, there were the most reptiles (257) that were considered lost. They also found 137 species of amphibians, 130 species of mammals, and 38 bird species.

Nearly 93% of the species were last found in the tropics, particularly in what the researchers termed “mega-diverse” countries. There were 69 species last spotted in Indonesia, 33 in Mexico, and 29 in Brazil.

The results were published in the journal Animal Conservation.

Anteaters to Woodpeckers

Researchers were intrigued by many of the lost species. Mooers mentions a spiny anteater (Sir David’s long-beaked echidna) that was last seen in 1961.

“The four spiny anteaters, plus the platypus, are the only mammals that lay eggs, and this tiny group is a very ancient offshoot of all other mammals,” he says. “Three of the four spiny anteaters alive today are at some risk of extinction, so it seemed pretty amazing to me that we do not even know if this one (which lives or lived in Indonesia) still exists.”

Mooers also found some of the lost birds fascinating.

“Everyone wants to know if the ivory-billed woodpecker is still alive, and Canada’s Eskimo curlew has not been confirmed extant since 1963 (when one was shot),” he says. “Another intriguing species (to me) is the New Caledonian owlet nightjar: This is a bird we identified almost a decade ago as being very special because it was both endangered and had no close living relatives. It seems it is also lost!”

An illustration of two ivory billed wood pecker
An illustration of two ivory billed woodpeckers. Imagezoo / Getty Images

The IUCN updates its list periodically and classifies a species as extinct when “there is no reasonable doubt that the last individual of a species has died.” This happens when “exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual.”

Only 75 of the 562 species that researchers recorded as “lost” are considered “possibly extinct,” Mooers says. But more than 100 are classified as “critically endangered.”

“Researchers believe some of these species will be found again—perhaps even most of them,  but we do not know what fraction,” he says. “The majority (417) are ‘data deficient,’ meaning we do not know their status.”

Mooers points out that 311 terrestrial vertebrate species have been declared extinct since 1500. That means 80% more species are considered lost than have been classified as extinct.

“This is really worrisome because if even a fraction of these lost species are really extinct, that extinct tally could go up a lot. That is the important part,” Mooers says.

“The fascinating part, to me, is that we do indeed rediscover species. I really like the idea that we don’t have all of nature under our control, that there are still species out there, doing their thing, and we and they are mutually oblivious. What saddens me most about the Anthropocene is that feeling that even nature will be, in some way, artificial.”

View Article Sources
  1. Martin, T.E. et al. "'Lost' taxa and their conservation implications." Animal Conservation. 16 May 2022. doi:10.1111/acv.12788

  2. coauthor Arne Mooers, a biodiversity professor at Simon Fraser University in British Columbia

  3. "IUCN Red List of Threatened Species." IUCN.