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Animal Ecologist Nicholas Rodenhouse | Meeting the Minds

Tuned in

Evidence that black-throated warblers use the grapevine to pick nesting sites upends conventional wisdom

Email|Print|Single Page| Text size + By Billy Baker
Globe Correspondent / July 21, 2008

NORTH WOODSTOCK, N.H. - It's just after 6 on a mid-July morning, and Nicholas Rodenhouse is doing what he does most every summer morning, trekking into the woods of the Hubbard Brook Experimental Forest to check on his beloved black-throated blue warblers.

As he makes his way through thick brush to a clearing, he stops for a moment to listen, hoping to hear a male singing. He's probably not the only one listening.

"Everybody sings early in the season," Rodenhouse explains, but mating season is wrapping up, and an important divide is starting to emerge. The males who have been unsuccessful in their procreation will soon stop singing, choosing silence over the blues. The proud papas, on the other hand, will continue belting out the tunes into August, broadcasting their success.

All around him, flitting stealthily between trees, Rodenhouse believes the young warblers born this year are listening, too. Over the next several weeks, they will eavesdrop on their elders, scouting several territories to make mental notes on who is singing and who is not.

And when they return from their Caribbean migration in the spring, they will use this bit of "public information" to make perhaps the most important decision of their lives: where to build their nest. As any realtor will tell you, it's all about location; in the case of the birds, that location will have a huge impact on their mating success.

They will need a good food source - they love caterpillars - and good vegetation to support and shelter the small, fragile nests they will build a few feet off the ground. And they need to keep an eye out for predators - chipmunks and red squirrels are the bad guys in their story - that will menace their eggs and young.

"We've always wanted to know what cues they used to make that decision," Rodenhouse said, explaining the problem. "Was it vegetation? Food sources? Characteristics of the neighborhood? Was it something they could measure?"

And so Rodenhouse and his team tried to think like a warbler, to evaluate and measure each habitat. They counted caterpillars. They stopped silently for five minutes and counted any potential predators they saw. They meticulously mapped the locations of all the nests, the number of eggs in them, the number of nestlings that hatched.

But a recent experiment at Hubbard Brook indicates that none of this matters to a young warbler looking for a good territory. Rodenhouse and some colleagues recently published a paper in the journal Proceedings of the Royal Society B: Biological Sciences overturning the decades-old conventional wisdom that held vegetative structure as the chief basis for a bird's habitat choice.

Instead, they believe the "blues" choose where to live based on recommendations from their peers. Sound familiar?

In the experiment, researchers recorded the songs of the successful males, and then played those songs after the mating season in a variety of different habitats, including those they knew to be very bad for the warbler's needs, such as a clear-cut forest. The following spring, more than 80 percent of the poor habitats had warblers in them (while the control group of poor habitats, where the researchers hadn't played any music, had zero birds). Researchers had given out bad recommendations, and the birds bought it.

"I didn't think it would work," Rodenhouse said of the experiment. "But by gum it did."

"By gum," like "by golly," is pure Rodenhouse. He's 55, from a small town on the shore of Lake Michigan, and the apple-pie-and-ice-cream Midwestern-wholesomeness oozes from his every sentence, like when he places his hands on his hips and takes a deep breath through his nose and says that his job is to go out in the forest early in the morning and just stand there and listen to the world.

He doesn't have to say anything else for you to know that he thinks this is the greatest thing ever - though at the moment he has chosen to avoid mentioning the part of his job, as a biology professor at Wellesley College, that involves classrooms and grading papers.

The Hubbard Brook Experimental Forest, an 8,000-acre ecological laboratory in the White Mountain National Forest, is a home-away-from-home for Rodenhouse, who specializes in the population biology of migratory songbirds. He has been coming here since the early 1980s, when he did his Dartmouth PhD research on the black-throated blue warbler - a tiny bird that lends itself to population study because its low nests are easy to monitor. And he has been a permanent summer tenant every summer since 1996, awakened at 5 a.m. each day by the loons next to his cabin on Mirror Lake.

His is, he says, not a field that lends itself to the eureka moment; it's about gathering information daily. "Trust the data" is a mantra posted in the barn that serves as the hub for the 17 members of Rodenhouse's "bird crew."

But this latest paper could be the closest thing to that eureka moment. If the birds choose their habitat chiefly on the recommendations of other birds, this could be a finding, Rodenhouse and others in the field say, with far-reaching implications, and represents particularly good news for birds' ability to adapt to a changing environment. By listening to their peers, the birds can avoid having to find out the hard way that a habitat has become unsuitable.

"One worry with climate change is that the old cues they use [to choose a habitat] might not work any more," said Robert Askins, a biology professor at Connecticut College. "The structure of the vegetation changes, and what was good may not be anymore. If this hypothesis is correct, this may not be such a serious problem because birds will find new habitats by finding other places birds have been successful. You won't need biological or organic evolution to occur; the population can respond through learning, and they can do that much more rapidly."

John Faaborg, a professor of avian ecology at the University of Missouri, thinks the finding could throw a wrench into the entire idea of wildlife management - in a good way. "With management, you try to provide the appropriate habitat. But sometimes you do this and the birds don't come." Using recordings of the post-breeding songs could be a good way to draw birds into unused suitable habitats, Faaborg said, though the generality of this finding may be limited, because not all species of songbird sing after breeding.

The idea of social cues being the deciding factor in habitat choice is "fascinatingly simple," according to Matt Betts, an assistant professor of forest science at Oregon State who was the lead author on the paper. And it has clear parallels to human behavior, where Internet review sites such as Yelp.com are having an increasingly powerful influence on what people decide to do and buy.

"I use the metaphor of choosing a coffee shop when you're new in a town," Betts said. "Are you going to go to the one with nobody in it, or the one that's hustley and bustley?"

Rodenhouse is excited by the hypothesis, but in his reserved way. There's only one sure-fire way to get him going, and as he walks down a trail he's been down a thousand times, it happens. Just a few feet to his right, he spots a knee-high nest in a patch of yellow birch saplings. He checks his maps, and it isn't listed.

"We may have just found a new nest," he said. On his face is the look of a guy who thinks he's got the greatest job in the world, by gum.

Fact sheet

Hometown: South Haven, Mich.; lives in Sherborn.

Education: Studied biology at Hope College in Michigan before being drafted in 1972. He went to the Army's Defense Language Institute and studied Hungarian before returning to Hope to finish his degree in 1977. Got his master's degree in animal ecology from Iowa State in 1981, and did his first study of black-throated blue warblers at Hubbard Brook to earn his PhD from Dartmouth in 1986.

Family: Wife, Marianne Moore, is a limnologist and an associate professor at Wellesley College. Their honeymoon was six weeks on a zooplankton expedition in the Australian outback.

Hobbies: Rodenhouse enjoys woodworking because he says he's too cheap to pay for furniture, and is currently hooked on restoring classic stereo speakers. He and his wife are also returning the land around their house - which was lawn when they bought it - back to its natural state.

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