Old growth could be key for native songbird species

According to reports, because of rising temperatures, the areas where hermit warblers can live and find food are shrinking by up to 4 percent each year. (National Audubon Society)

BLUE RIVER, Ore. — Hotter, drier summers are having an impact on some of the migrating songbirds that come to Oregon and Washington to breed each spring.

Oregon Public Broadcasting reports that because of rising temperatures, the areas where hermit warblers can live and find food are shrinking by up to 4 percent each year. Now researchers with Oregon State University are developing an experiment to track the tiny songbirds through the Pacific Northwest.

OSU researchers have already found that warbler populations declined in areas with young forests but in some cases increased in old growth forests despite the warming climate. Researchers Hankyu Kim and Adam Hadley are conducting a new experiment to determine why the warblers are doing better in old growth areas.

Kim has gotten inside the head of the hermit warbler. He knows what makes the tiny songbird tick.

“These birds are territorial in the breeding ground, they set up their territories and they fight with each other to defend it,” he said.

Kim uses a nearly invisible net strung between two fishing pools, a plastic warbler decoy and a looping bird-call recording to lure hermit warblers so they can be captured, tagged and released. The tiny radio tag allows Kim and Hadley to track the birds through the dense forests of the Oregon Cascades.

They hope to determine how the birds use the forests and whether they use the temperature variations between the top and the bottom of the forest canopies to mitigate the effects of climate change.

Hadley says it’s possible that when it’s warmer, the birds stay to the bottom and more shady parts of the trees.

Learning how the birds move could help explain how warblers and other species deal with rising temperatures.

“We have these long-term population monitoring routes across the Northwest. And a surprising number of species are declining,” said OSU professor Matt Betts. “Actually, more than about half of the species that live in a forest like this are in decline.”

Earlier research by OSU’s Betts and Sarah Frey found warblers declined in areas with young forests, including those replanted after clear cut logging. But hermit warblers are doing better in other areas.

“In landscapes that had more older forest, their population declines were lowered, or even reversed, even though the climate has been warming,” Frey said.

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