A recent study indicates that the International Union for Conservation of Nature (IUCN) Red List, a database of endangered species, seems to underestimate the number of species at risk. About 200 forest bird species from six of the world most biodiverse are at risk of extinction. On the other hand, in IUCN the species is listed as non-threatened.

The findings of the study were printed in Science Advances. Stuart Pimm, the co-author of the study and Doris Duke Professor of Conservation Ecology at Duke's Nicholas School of the Environment, said that the Red List employs rigorously objective criteria, is transparent and is democratic in soliciting comments on species decisions. He further said that its methods are seriously outdated.

The study involved 586 bird species from Central America, Atlantic Forest of Brazil, Madagascar, Western Andes of Colombia, Southeast Asia and Sumatra. The team of researchers included geospatial data on the elevational preferences of the birds. Then, they added data on the forest cover remaining for the birds to gauge the amount of suitable habitat remaining within their distributions.

Based on their refined ranges, 210 bird species are in a higher threat category. On the other hand, the IUCN listed 108 species at risk of extinction. One example of the bird species is the gray-winged cotinga found in Brazil. It is listed as vulnerable on the IUCN Red List. On the other hand, in the study, its refined range size is smaller than 100 square kilometers that must be categorized as critically endangered, according to Mongabay.

Furthermore, the researchers theorize that the finding would probably expand to mammals and amphibians. Meanwhile, the IUCN disagrees on the study. Stuart Butchart, the head of Birdlife International and oversees the Red List's birds, said that the study is "fundamentally flawed."

He further explained that in the study, they use the various set of metrics than the IUCN. He also said that the IUCN uses a broad habitat range, while the study uses much narrower criteria, as noted by Smithsonian.