Scientists work hard to avoid declaring a species extinct

Lonesome George was long considered the last Pinta Island tortoise, but genetic testing suggests there may be a few others like him.
Lonesome George was long considered the last Pinta Island tortoise, but genetic testing suggests there may be a few others like him. (Alamy)

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By Brian Palmer
Monday, February 21, 2011; 1:44 PM

As a child in the 1980s, I was convinced that an ecological disaster was imminent. Scattered into my afternoon television programs were commercials about the dangers of soil erosion and acid rain. The scariest of all were ads showing some furry, wide-eyed primate, followed by the warning: "Extinction is forever."

It was an ominous warning for a kid who didn't quite understand what "forever" meant. (My list of things that lasted forever at that time included tooth brushing and church.) But it got me wondering: How do they know a species is extinct? And who gets to make that call? Is there a Supreme Court for extinction out there?

Well, sort of. The International Union for Conservation of Nature's Red List serves as the recognized authority on species population status. The group assigns conservation labels-"least concern," "near threatened," "vulnerable," "endangered," "critically endangered," "extinct in the wild" and "extinct" - to the world's wildlife. But the organization's experts don't like to think of themselves as arbiters of extinction.

"The main focus of the Red List is to stop species from going extinct - to identify species moving in that direction and to marshal resources to protect them," says Craig Hilton Taylor, unit manager of the Red List. "But, by default, we became the standard international list for extinctions."

The Red List has assigned monitoring responsibility to a series of conservation authorities. For example, there are 29 organizations tracking mammals, including one that handles anteaters, sloths and armadillos, one that surveys bat populations and two that catalogue elephants.

The mammals get the most attention, by far. One group, Birdlife International, handles the world's birds even though there are twice as many known bird species (up to 10,000) as mammal species (fewer than 5,000).

These scientific authorities are supposed to conduct an assessment of all the animals in their purview at least every 10 years. But that's a pretty tall order, and the program has a long way to go.

"There are between 1.8 and 2 billion described species worldwide," notes Hilton Taylor. "We haven't yet looked at 57,000 of them."

So how do you count animals in the wild? It really depends on the creature. Some critically endangered birds, for example, are territorial. All it takes is binoculars and patience. For wide-ranging creatures, counting requires more creativity. Scientists use migration patterns and birthing habits to monitor certain whale species, for example. They conduct aerial photographic surveys of breeding waters, looking for newborns. Then they use data about what proportion survive to adulthood to calculate the health of the population.

For a species to get a Red List classification, conservation scientists must complete two surveys. The researchers submit a map of the species's range, a list of its preferred habitats, the major threats against it and a projection of the population trend. Once a species is found to be threatened, the assessments become a regularly repeated process, with the Red List encouraging more-frequent surveys to monitor conservation progress.

There are no rigid criteria, such as the number of years since last sighting, for declaring a species extinct. But the Red List doesn't make the decision lightly.

Consider the case of the Yangtze River dolphin, a long-beaked, nearly blind cetacean also known as the baiji, that inhabited about 1,000 linear miles of a single river in southeast China. While many believe there were thousands of specimens in the wild in the middle of the 20th century, a Chinese scientist completed the first formal population survey only in 1982. He estimated that there were around 400 individuals. On the basis of that survey, the dolphin was classified as endangered by a predecessor to the Red List in 1986.


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