Are there more endangered bird species than we think?

Hundreds of bird species around the world are endangered even though they’re not classified as such, according to a new study. Using geographical data, scientists analyzed the habitats of certain birds and concluded that the International Union for Conservation of Nature’s Red List — the definitive guide to endangered animals — underestimates the risk for 210 bird species. Red List officials disagree with the findings, saying that the new calculations are wrong and the study is “fundamentally flawed.”

The Red List is the most comprehensive database used to assess biodiversity. It was developed about two decades ago, before there was widely available satellite data, and classifies animals as “vulnerable,” “endangered,” or “critically endangered.” Those classifications are in part based on how much habitat is left for a specific species — less than 20,000 square kilometers, 5,000 square kilometers, or 100 square kilometers. But according to study co-author Stuart Pimm, a professor of conservation ecology at Duke University, the IUCN’s methods are outdated. “IUCN is still holding onto a method of assessing species that’s 25 years old that doesn’t account for this new technology,” Pimm says.

This method could be more accurate than the old guidelines

To more accurately calculate the habitat size for 586 species in six areas around the world, Pimm’s team combined data on bird distribution range, elevation, and forest cover. The researchers found that the habitats of many birds are smaller than had been previously estimated. In fact, about 210 bird species should be in a higher “threat category” than they currently are, according to the study. “While that’s bad news, we’ve got to be better prepared and need to know which species are at risk,” says Pimm, “so having better information means we have a better chance of saving the species from going extinct.” He hopes that IUCN will reassess its classifications of birds because not doing so could put many in danger.

Natalia Ocampo-Peñuela

But IUCN officials disagree. The paper is “fundamentally flawed,” Stuart Butchart, the head scientist of BirdLife International, the Red List bird authority, wrote in an email to The Verge. Pimm’s calculations are based on a different habitat range, that’s why the results are skewed, Butchart says. The IUCN’s methods are perfectly sounds, he says, they’re just based on different metrics.

When the IUCN is calculating an animal’s habitat, it takes into account the broad habitat range, not the narrower habitat range where the animal is most likely to actually live, Butchart says. Imagine you’re trying to figure out the habitat of the robin in Manhattan: you can either consider all of the island as the habitat range, or you can take into account only Central Park, where robins are actually most likely to live. The different metrics lead to different results, Butchart says.

The important thing is that we have new ways of measuring habitat ranges

Today’s study is basing its findings on the narrower range — Central Park — but that means that the calculations are so narrow that they overestimate the danger the birds are in, according to both Butchart and IUCN Senior Scientific Officer Michael Hoffman. “They are generating these results where they predict that we have underestimated extinction risk because they are looking at the wrong measure,” says Hoffman.

But Pimm defends his study, saying that the calculations in his paper could be a new and more practical measure of habitat that can be used instead. Because it incorporates more data, it will be more accurate than the old guidelines.

All of this sounds like “an issue of semantics,” says Wesley Hochachka, assistant director of bird population studies at the Cornell Lab of Ornithology. There’s little point in being fixated on comparing metrics, Hochachka says. The key takeaway is that we need to use the latest data we have when considering habitat ranges and whether species are at risk of extinction. “When the IUCN was coming up with [the Red List] criteria, we didn’t have the capability of doing what Pimm and his colleagues have done in his paper,” he says. “The most important point is just saying that we now have the capability to do a whole lot better at defining the ranges in which species actually live, and we should use that information.”