美国国家公共电台 NPR Old-Growth Forests May Help Songbirds Cope With Warming Climate

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LULU GARCIA-NAVARRO, HOST:

Songbirds have been in decline for decades. And it's becoming clear that climate change is a factor. Now scientists are finding that old-growth forests may help the birds cope with rising temperatures. Jes Burns of Oregon Public Broadcasting and EarthFix explains.

JES BURNS, BYLINE¹: Researcher Hankyu Kim and his colleagues are developing a new experiment in Oregon's Cascade² Mountains. They're seeing if they can catch, tag and then track the movements of a tiny, yellow-headed songbird called the hermit³ warbler.

HANKYU KIM: These birds are territorial⁴ in the breeding ground. They set up their territories. And they fight with each other to defend it.

BURNS: Armed with this knowledge, a nearly invisible net, a lifelike decoy and a loop of recorded bird call...

(SOUNDBITE OF BIRD CHIRP)

BURNS: ...The Oregon State University researchers' trap is set.

KIM: So when birds fly in, they hit the net and drop down into a pocket and lie down there like a hammer.

BURNS: And within just a few minutes, the hermit warbler takes the bait.

UNIDENTIFIED PERSON #1: He's in.

UNIDENTIFIED PERSON #2: Another win for the decoy.

BURNS: Learning how the warblers move could help explain how bird species are dealing⁵ with rising temperatures and climate change.

Matt Betts studies birds at Oregon State.

MATT BETTS: We have these long-term population monitoring routes across the northwest. And a surprising number of species are declining, actually more than about half of the species that live in a forest like this are in decline.

BURNS: For the hermit warbler, those declines are up to 4 percent each year. Rising temperatures can shrink where some birds can live and where they can find food. Research by Betts and Sarah Frey found warblers declined in areas with young forests, including those replanted after clear cut logging. But...

SARAH FREY: In landscapes that had more older forests, their population declines were lowered or even reversed even though the climate has been warming.

BURNS: The warblers thrived in areas with old growth. They think the reason is, in part, because these forests are cooler than younger forests, up to five degrees cooler. And the hermit warblers use this to their advantage. Now, they want to try to prove it. And that's where this new study comes in.

ADAM HADLEY: Transmitter 12, frequency 357.

BURNS: Adam Hadley and Hankyu Kim move the trapped hermit warbler's feathers aside to attach a tiny radio tag to its back using non-toxic glue.

KIM: It's an eyelash glue.

HADLEY: For gluing fake eyelashes on. If it works on people, I guess...

KIM: For a month.

HADLEY: ...It works on the skin of birds, too.

BURNS: The bird flies away.

The next day is the true test. Hadley and the others push into a dense⁶ stand of trees armed with receivers that look like old-fashioned TV antennas⁷.

HADLEY: It's going away from us.

BETTS: We'll try and be as quiet as we can.

BURNS: They want to compare the bird's movements to temperature data they've been gathering⁹ at different levels in canopy¹⁰.

HADLEY: Given the differences in temperature across the whole height of a tree, it's possible that when it's warmer they may be only using the bottom in more shady parts of the trees.

BURNS: The complex layers and sheer biomass of old growth keeps the temperature low. Hadley waves the antenna⁸ through the air trying to pinpoint¹¹ the warbler's location.

HADLEY: I'm not getting the strongest signal at the top of the tree. Seems to be a bit stronger in the mid-canopy.

BURNS: If Hadley, Matt Betts and the others are able to track the hermit warblers through these forests, they'll get another step closer to understanding how native species might cope with rising temperatures.

BETTS: Don't see it likely that hermit warblers will have air conditioning anytime soon.

BURNS: But it looks like old-growth forests could be the next best thing. For NPR News, I'm Jes Burns in Blue River, Ore.

(SOUNDBITE OF ANDREW BIRD SONG, “SOVAY”)

GARCIA-NAVARRO: And that story came from NPR's energy and environment team.