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A songbird's fate hinges on one fragile area

June 19, 2019

COLUMBUS, Ohio - Researchers were surprised to find that a migratory songbird that breeds in the eastern and central United States is concentrated during winter in just one South American country.

The study found that 91 percent of 34 Prothonotary Warblers fitted with tracking technology at six U.S. breeding sites spent their winter in northern Colombia - an area just 20 percent the size of their breeding range.

In addition, nearly all the warblers stopped over at three locations in the Yucatan Peninsula and Central America on their migration between the United States and Colombia, the study showed.

The results are concerning because they suggest the fate of the Prothonotary Warbler may depend on protecting habitat in a small area that is threatened with deforestation, said Christopher Tonra, lead author of the study and assistant professor of avian wildlife ecology at The Ohio State University.

"It was surprising to us how consistently Prothonotary Warblers from all over the United States ended up in Colombia," Tonra said.

"It speaks to how important habitat protection in this one country is to the overall population."

The study will be published June 19, 2019 in the journal The Condor: Ornithological Applications.

Prothonotary Warblers are considered a "species of concern" nationally, and in many states because of population declines during the 20th century.

The researchers used a relatively new technology called geolocators to track the birds. Researchers captured Prothonotary Warblers at their breeding sites in six states - Wisconsin, Ohio, Virginia, South Carolina, Arkansas and Louisiana - and attached the tiny devices to them.

The geolocators' light sensors detect the length of day, which gives researchers an approximation of the birds' latitude as they moved south and north. They also have clocks, which can help estimate the birds' longitudinal position as they move east or west through different time zones.

When the birds arrived back at their breeding grounds the following spring, the researchers recaptured them and downloaded the data their geolocators had collected, which showed approximately where they had spent the winter and the route they took to get there and back.

The researchers were surprised that no matter where the Prothonotary Warblers bred in the United States, they almost all ended up in Colombia. In other species of migratory, neotropical birds, populations that breed in different areas of North America often winter in different parts of Central and South America, Tonra said.

"We didn't expect that Prothonotary Warblers from all around the United States would use the same wintering region," he said.

"It shows the importance of using modern technology like geolocators to give us a clearer view of the lives of migratory songbirds."

Also important was the finding that nearly all the birds spent a significant amount of time on their migratory journey at stopover locations in the Yucatan Peninsula, and along the border between Honduras and Nicaragua and between Costa Rica and Panama. They fed there to gain the energy to complete their journey.

"This was something we really didn't know before this study, and another reason why the use of geolocators was so crucial," Tonra said.

"In addition to the breeding ground and wintering grounds, they have these very critical refueling sites that need our attention and protection."

While the fact that Prothonotary Warblers are concentrated in relatively small refueling and wintering areas is concerning, it also offers opportunity, Tonra said.

"It means that we can have a large positive impact by protecting habitat in specific regions," he said.
Tonra conducted the study as part of a collaborative working group, founded by Erik Johnson of Louisiana Audubon Society, that also included individuals from the Smithsonian Migratory Bird Center, Arkansas State University, Virginia Commonwealth University, the U.S. Fish and Wildlife Service and South Carolina Audubon.

Contact: Christopher Tonra,

Written by Jeff Grabmeier, 614-292-8457;

Ohio State University

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