How do we decide if an animal is extinct?

Extinction. How would you define it?

For Oxford Dictionaries, it’s a species “having no living members.”

So far, straightforward. Even so, the central challenge is not defining what being extinct means, but judging when a species has finally lost its battle to survive. That is a complex and lengthy process, involving reams of data, complicated mathematical models and finely balanced calls. And it’s one that’s becoming knottier as biodiversity loss accelerates.

Human impact

“The planet is in the midst of the Earth’s sixth mass extinction. And we are the driving factor,” International Union for Conservation of Nature (IUCN) Director-General Inger Andersen said in February. “Species can be brought back from near the brink of extinction through good conservation and protection investments, through sound policies and smart interventions. But once a species is extinct, it is forever, and there is no coming back.”

Accurately measuring and defining species that are in trouble forms a key piece of conservation work.

While the IUCN Red List of Threatened Species, which began in 1964, does much of the heavy lifting, its assessment categories show just how thorny the issue is. Several different ranks exist including “extinct”, “extinct in the wild” and “possibly extinct” as well as “critically endangered (possibly extinct)”, and “critically endangered (possibly extinct in the wild)”.

After looking at more than 96,500 species, IUCN estimates more than 26,500 are threatened with extinction, including 40% of amphibians and 25% of mammals. The “possibly extinct” list includes Indonesia’s Aru flying fox – a species of megabat with no recorded sightings since 1992 – and the Christmas Island shrew, last spotted in 1985.

These nuances underscore how arduous and fallible the process is, and it helps to explain why years of careful monitoring and planning can still result in error. Recently a thought-to-be-extinct giant tortoise was uncovered in the Galapagos Islands.

“To find a living tortoise on Fernandina Island is perhaps the most important find of the century,” said Wacho Tapia, Director of the Giant Tortoise Restoration Initiative. “The only live specimen of the species from Fernandina was found 112 years ago.”

Spotting a leopard

It’s not the only case of something springing up where it wasn’t expected. A black leopard was photographed in Kenya this year – the first confirmed sighting in Africa since 1909.

These animals coming back from the brink – others may become extinct before they’ve even been discovered – provide an illustration of the challenge facing those seeking to quantify the losses.

In the end, the accuracy of such lists comes second to raising awareness. Seeking to apply data and numbers to nature’s destruction is about painting as full a picture as possible, to inform better planning and policy making and to raise awareness. Environmental issues and caring for the natural world were key themes at this year’s World Economic Forum Annual Meeting in Davos.

The Forum’s Global Risks Report 2019 said humanity was “sleepwalking its way to catastrophe” citing extreme weather, failure to act on climate change, and natural disasters as key risks. Alongside these mounting hazards, there’s an increasing awareness of a need to act.

“The IUCN Red List tells us where we ought to be concerned and where the urgent needs are to do something to prevent the despoliation of this world,” Sir David Attenborough said. “It is a great agenda for the work of conservationists.”