Study Doubles Estimate of World Bird Species

by AMNH on

Research posts

Think you know birds? Think again. A new study of morphology and genetics suggests previous research may have underestimated bird biodiversity by as much as half, not counting thousands of previously undescribed species that are hiding in plain sight. The Museum-led research, published this week in the journal PLOS ONE, sheds new light on this group of animals, with major implications for conservation practices around the world.


Kinglet perches on a concrete ledge edged with wire fencing.
The Golden-crowned Kinglet (Regulus satrapa) was among the birds examined in the team’s morphological study.
Creative Commons/D. Daniels

“We are proposing a major change to how we count diversity,” said Joel Cracraft, an author of the study and a curator in the Museum's Department of Ornithology. “This new number says that we haven’t been counting and conserving species in the ways we want.”

Traditionally, bird species have been counted using the “biological species concept,” which defines species as animals that can breed together. Using this technique, ornithologists long estimated a count of between 9,000 and 10,000 species of birds worldwide. This model, though, was in dire need of an update.


Tawny eagle peers majestically from its treetop perch on a branch.
Researchers may have a lot more to learn about birds like the Tawny Eagle (Aquila rapax).
Creative Commomns/Y. Krishnappa

“It’s really an outdated point of view, and it’s a concept that is hardly used in taxonomy outside of birds,” said lead author George Barrowclough, an associate curator in the Museum’s Department of Ornithology.

Cracraft, Barrowclough, and their colleagues at the University of Nebraska, Lincoln, and the University of Washington examined the morphology—physical characteristics like plumage pattern and color—of 200 randomly selected bird species. The new reading showed that more than 40 percent of these species could represent two or more evolutionary lines. That means bird biodiversity is likely closer to 18,000 species worldwide.

The research team also conducted genetic studies of 437 traditionally recognized bird species, chosen because there were already suspicions that they could be broken down into more species. The study suggests these concerns were well grounded—those 437 species look more like over a thousand under further analysis.


Red-shouldered Hawk sits on a rocky outcropping and peers into the distance.
Researchers conducted genetic analyses of hundreds of species, including the Red-shouldered Hawk (Buteo lineatus).
Creative Commons/M. Baird

The potential doubling of the number of bird species isn’t just a matter for taxonomists and other scientific record keepers, the authors point out. It also has massive implications for conservation efforts surrounding these animals.

“We have decided societally that the target for conservation is the species,” said Robert Zink, a co-author of the study and a biologist at the University of Nebraska, Lincoln. “So it follows then that we really need to be clear about what a species is, how many there are, and where they’re found.”