The world’s most widely used database of endangered species — the International Union for Conservation of Nature (IUCN) Red List — classifies species according to their risk of extinction. But this list underestimates the number of species at risk, concludes a new study.
Nearly 200 forest bird species from six of the world’s most biodiverse places are at immediate risk of extinction despite being deemed non-threatened in the IUCN Red List, researchers report in a new study published in Science Advances.
“The Red List employs rigorously objective criteria, is transparent, and democratic in soliciting comments on species decisions,” Stuart Pimm, study co-author and Doris Duke Professor of Conservation Ecology at Duke’s Nicholas School of the Environment, said in a statement. “That said, its methods are seriously outdated.”
The IUCN database uses various criteria to assess the extinction risk of a species. One of these criteria is the extent of occurrence, or the “area contained within the shortest continuous boundary encompassing all the known, inferred or projected sites of occurrence of a species.” Based on their extent of occurrence or range, species are classified into various threatened categories — vulnerable, endangered or critically endangered.
The new study “refines” the original ranges for 586 bird species from Atlantic Forest of Brazil, Central America, Western Andes of Colombia, Madagascar, Sumatra, and Southeast Asia. To create these refined ranges, Pimm and his team included geospatial data on the elevational preferences of the birds, and then added data on the forest cover remaining for the birds to calculate the amount of suitable habitat remaining within their distributions.
Of the 586 bird species included in the study, the IUCN lists 108 species as being at risk of extinction. But based on the refined ranges, 210 bird species belong in a higher-threat category than their current Red List classifications, the study found. The grey-winged cotinga (Tijuca condita), for example, is a bird found in Brazil that is currently listed as vulnerable in the Red List. But its refined range size, according to the study, is smaller than 100 square kilometers (~39 square miles), which should shift its threat category to critically endangered.
The refined range sizes also indicate that 189 species, which are currently classified under lower-risk categories of least concern or near threatened, should be classified as vulnerable, endangered or critically endangered on the IUCN Red List, the study found. Moreover, most of the bird species have less than 10 percent of their range within protected areas, the researchers report.
“A lot of birds that don’t have their range protected are birds that are currently not classified as threatened,” study’s lead author Natalia Ocampo-Peñuela, who received her Ph.D. from Duke earlier this year, told Mongabay. “We have birds that have smaller ranges than we think because of habitat loss, and their ranges are also not protected. So we are not putting them in the right threatened category, and we are not spending resources for conservation of these species. They could go extinct before our eyes and we wouldn’t know it.”
The study’s overall approach of using high resolution maps and data to examine the extent of suitable habitat within the species ranges is sound and makes the most of available data, said Stuart Butchart, head of science for BirdLife International in Cambridge, UK, an organization that assesses the extinction risk for the world’s birds for the IUCN Red List. “Unfortunately, the application of these data to the IUCN Red List criteria is flawed,” he told Mongabay.
Butchart said that the authors incorrectly applied their estimates of refined ranges to the thresholds for extent of occurrence. Instead, the study should have applied their estimates to the thresholds for another criterion called the area of occupancy. This criterion excludes areas unsuitable or unoccupied by the species, and is a subset of the species’ extent of occurrence. “The significance of this is that the thresholds for each threatened category for Extent of Occurrence are an order of magnitude larger, so it is unsurprising that they found lots of species listed in categories of lower extinction risk on the published Red List than their analysis suggested,” he added.
Ocampo-Peñuela agrees that the refined ranges produced in the study is not the same as the Red List’s extent of occurrence. “But they’re also not really the area of occupancy,” she said. “We make the ranges that have the highest probability of the species being there but we cannot say that the species is there for certain. So if we had a different threshold that was like a refined extent of occurrence, that would be ideal.”
Ocampo-Peñuela added that the goal of the study is to encourage the IUCN to include technological information to make their Red List assessments better. Mapping the remaining habitat of species should be an essential part of the current Red List criteria, the study concludes.
“The authors will be pleased to hear that this is already planned,” Butchart said. “The extent of suitable habitat has already been assessed for all of the world’s 11,000 forest-dependent birds, mammals and amphibians, and the estimates applied correctly to the Red List criteria, with the implications already being incorporated into ongoing efforts to reassess all these species over the next couple of years.”
- Ocampo-Peñuela, C.N. Jenkins, V. Vijay, B.V. Li, S. L. Pimm. Incorporating explicit geospatial data shows more species at risk of extinction than the current Red List. Sci. Adv. 2, e1601367 (2016).
Correction 11/10/2016, 05:15 am Eastern: The original version of this story incorrectly stated that Dr. Natalia Ocampo-Peñuela was a co-author of the study. She is in fact the lead author of the study and we have corrected the sentence. We regret the error.