JUANA SUMMERS, HOST:
In 1969, a team of researchers mapped the territories of songbirds inhabiting a patch of forest in central New Hampshire. For more than half a century, that work has continued, revealing insights about the birds and their changing home. Science reporter Ari Daniel went to visit.
ARI DANIEL, BYLINE: The patrol begins every morning. It's late June, and I follow Miranda Zammarelli, a Ph.D. candidate at Dartmouth College and a behavioral ecologist, into the Hubbard Brook Experimental Forest.
MIRANDA ZAMMARELLI: If you look ahead, you'll see a tree that says A1 on it.
DANIEL: It's got that pink ribbon around it.
ZAMMARELLI: Yes. That tree is just an indicator that we're on the plot now.
DANIEL: We're standing at the northeast corner of a 25-acre grid, which is basically Zammarelli's outdoor office.
ZAMMARELLI: Now that I'm on the plot, my job is just to sort of wait till I hear this next bird and then try to accurately pinpoint where that bird is.
DANIEL: So you just kind of wander and wait and listen.
ZAMMARELLI: Yes.
DANIEL: OK. In we go.
(SOUNDBITE OF BLACK-THROATED BLUE WARBLER CALL)
ZAMMARELLI: Did you hear that?
DANIEL: Yeah.
ZAMMARELLI: That's a black-throated blue warbler. So I'm going to mark him.
(SOUNDBITE OF BLACK-THROATED BLUE WARBLER CALL)
DANIEL: Zammarelli uses a mapping app on her phone to input the location of the bird based on where she's just heard him. The warbler's small enough to fit in the palm of her hand, but this is breeding season, and he's got something big to say. So do other warblers in the forest.
ZAMMARELLI: They're basically having what I call a territorial rap battle. Hey, this is my space, stay away. And the other bird's like, no, this is my space, stay away. And they're singing back and forth, trying to claim, like, their spot.
DANIEL: That spot is where the bird will attract his mate and raise his young, so high stakes. Zammarelli and others have been mapping these territories for the last month and a half, documenting where some two dozen species of songbirds are located. The researchers say the birds play important roles in their ecosystem. They're high up in the food web, and they help disperse seeds and eat insects. The territory maps, they go back decades. Before the cell phone app, they were all sketched by hand.
DICK HOLMES: We have maps for every species for each of the 57 years.
DANIEL: Dick Holmes, who's here in the forest with us, as well, unfolds one of the paper maps. He launched this whole thing back when he was just starting out as a biologist at Dartmouth. Today, he's almost 89 and a professor emeritus.
HOLMES: So all the observations, you add them up from day to day, and you end up with a seasonal pattern showing all the different territories on the plot.
DANIEL: Those territories are delineated by circles on the maps, crisscrossed by a swarm of arrows and dotted lines. In the beginning, Holmes had a fairly simple question. How do songbirds fit into the food web of the forest? As he and his team gathered more information on the birds year after year, their questions evolved.
HOLMES: We got interested in what determines the number of birds, and why are their numbers increasing or decreasing?
DANIEL: For instance, the researchers heard a bird called the least flycatcher on the plot for the last time in 1994, and the American redstart, a jet-black little fella with orange splashes, pretty much stopped breeding here in the early 2000s. The primary reason, says Miranda Zammarelli, appears to be that the forest, which had been clear cut a century ago and then left to regrow undisturbed, has been aging and changing ever since.
ZAMMARELLI: It's naturally growing, and we're seeing how the bird communities change as a result of this natural growth.
DANIEL: That is, the ups and downs of these little songbirds have revealed how the forest around them has grown up, a result that matches work done elsewhere. This field site's yielded over 200 scientific publications, all of which depended on poring over those paper maps until Zammarelli began her Ph.D. a few years back and her advisor asked if she knew anyone who could digitize them.
ZAMMARELLI: I was like, I can do it. I had digitized collections before.
DANIEL: And getting the 50-plus years of maps into the computer enabled Zammarelli to bring the data to life in a new way.
ZAMMARELLI: So that allowed us to look at how these birds are using the space and also how big of a territory they're occupying in the habitat.
DANIEL: In a paper published in Ecology Letters, Zammarelli and her colleagues found that birds, no matter the number, divide the habitat up equally. It's a finding made possible by decades of mapmaking.
ZAMMARELLI: I think about all the hands these maps touched. I feel very grateful to be part of a system that has been, you know, going on for over 50 years.
DANIEL: In his view, Holmes says that we're in a moment of great environmental change, which makes a long-term study like this one more important than ever. But he says the project's in a precarious place with the federal government slashing science budgets.
HOLMES: It's hard to tell what's going to happen in the next few years.
DANIEL: But at least for the next few minutes, Holmes and Zammarelli know exactly what'll happen. The birds will continue to layer the air with melody, singing the collective song of their forest.
(SOUNDBITE OF BIRD CHIRPING)
DANIEL: For NPR News, I'm Ari Daniel, Woodstock, New Hampshire.
(SOUNDBITE OF AMIE BLU SONG, "EVERYTHING ABOUT HER") Transcript provided by NPR, Copyright NPR.
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