Russet-crowed warbler at Pantaicolla Ridge in Peru
The russet-crowned warbler, seen here in the Pantiacolla Ridge in Peru. This tropical bird species has shifted its habitat approximately 80 meters upslope to avoid warming temperatures. Credit: Graham Montgomery

Around the world, species are fleeing warming temperatures from climate change. For those living on mountains, however, they face a hard truth: Once they’ve retreated to the top of a mountain, they may have nowhere left to go.

Tropical birds are particularly at risk to rising temperatures. The birds are born, live, and die within the same section of woods, and they don’t migrate like temperate bird species often do.

Tropical birds living at high elevations are disappearing, and temperature increases are to blame.

Now, researchers have found that tropical birds living at high elevations are disappearing and that temperature increases are to blame. The study, which retraces the steps of a survey in Peru conducted 30 years ago, pinpoints local extinctions that are already occurring because of a warming climate.

Of the 16 species of tropical birds that previously lived at high elevations in the study area, “we failed to find 8 of the 16,” Ben Freeman, first author of the study and a postdoctoral fellow at University of British Columbia in Vancouver, Canada, told Eos. The results published yesterday in the Proceedings of the National Academy of Sciences of the United States of America.

Metaphors for Extinction

Ecologists coined the term “escalator to extinction” to describe the plight facing mountain species fleeing upslope. “It’s catchy, and it makes sense,” said Freeman. “But in my reading of the literature, there wasn’t much previous evidence that the metaphor is valid.”

Pantiacolla Ridge and Palotoa River in Peru
The Pantiacolla Ridge in southeastern Peru looms in the distance, with the Palotoa River in the foreground. The ridge is home to many species of tropical birds, some of which are disappearing because of rising temperatures. Credit: Graham Montgomery

In the latest study, Freeman and his colleagues traveled to southeastern Peru to a site called the Cerro de Pantiacolla, which was studied previously in 1985. The area warmed by 0.43°C in the intervening years, with little change to land use in the area. The researchers counted the birds by netting them and by recording their songs. The latter allows researchers to pick out individual birds’ voices in the absence of visual sightings. The team then compared their findings to the historical data.

Upslope Losses

With the modern-day numbers in hand, the researchers found that many of the species had relocated to higher ground. Of the 65 species surveyed, 43 of them had “shifted upslope,” the study finds. And as the researchers suspected, the birds that had previously lived at the highest elevations were the most vulnerable to disappearance.

Ben Freeman holds an Andean Cock-of-the-rock bird on Pantiacolla Ridge in Peru
Ecologist Ben Freeman holds an Andean cock-of-the-rock during field work on Pantiacolla Ridge in Peru. Credit: Graham Montgomery

“Nearly all of them are shrinking in size and declining in abundance, and some of them have disappeared,” Freeman said. “I was very surprised that the signal was so strong.” Of the 16 species found in 1985, 8 were nowhere to be found in the latest survey, and the researchers believe that 4 of those species are locally extinct from the site.

As the authors write in their paper, “high-elevation birds on the Cerro de Pantiacolla are indeed riding an escalator to extinction.”

One Mountain or a Worldwide Trend?

For Freeman, the results describe an ecosystem losing its richness. But does this directly affect people? “For me, I’d be hard pressed to make a raw economic argument that somehow life is worse for people with those four species gone,” he said.

“I think it really comes down to ethics, and aesthetics, that the world is a more vibrant and interesting place with these species in it,” Freeman added.

“This study is our worst-case scenario come true.”

Morgan Tingley, an assistant professor at the University of Connecticut in Storrs who was not involved with the study, said that the research confirms scientists’ fears. “This study is our worst-case scenario come true. It shows that even just a half degree Centigrade of warming can lead to species extirpations,” Tingley told Eos.

But Tingley cautions against applying these results to a broad area. “This study was done on one isolated mountain, so there could be something just odd or atypical about that site,” Tingley noted. “We need to scour the planet to see if this is happening elsewhere.”

—Jenessa Duncombe (@jenessaduncombe), News Writing and Production Intern 


Duncombe, J. (2018), Peruvian mountain birds take an “escalator to extinction”, Eos, 99, Published on 30 October 2018.

Text © 2018. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.