A Great Migration

  • Vermont Center for Ecostudies employees, from left, Melissa Mackenzie and Shelly Melendy, and volunteers Liz Lackey and Spencer Hardy, watch the sun rise from the top of the Mount Mansfield Toll Road. On their last trip to the mountain for the year, biologists opened their nets at 5:30 a.m. to gather data on thrushes, warblers and other birds as they begin their migration south for winter.Valley News photographs — James M. Patterson

  • Vermont Center for Ecostudies Executive Director Chris Rimmer holds a Bicknell's Thrush after removing it from a mist net on a section of the Long Trail that traverses Mount Mansfield in Underhill, Vt., on Sept. 16, 2015. Fifteen of the rare and declining Bicknell's Thrushes were captured and recorded that morning. (Valley News - James M. Patterson)

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  • From left: Vermont Center for Ecostudies Executive Director Chris Rimmer carefully removes a blackpoll warbler from one of 23 mist nets his team of conservation biologists set at the top of Mount Mansfield. They captured, recorded and released 82 birds, representing 16 species; A juvenile blackpoll warbler is held after being banded and recorded; Rimmer takes a blood sample from a Bicknell’s thrush.

  • From left: Vermont Center for Ecostudies Executive Director Chris Rimmer carefully removes a blackpoll warbler from one of 23 mist nets his team of conservation biologists set at the top of Mount Mansfield. They captured, recorded and released 82 birds, representing 16 species; A juvenile blackpoll warbler is held after being banded and recorded; Rimmer takes a blood sample from a Bicknell’s thrush.

  • From left: Vermont Center for Ecostudies Executive Director Chris Rimmer carefully removes a blackpoll warbler from one of 23 mist nets his team of conservation biologists set at the top of Mount Mansfield. They captured, recorded and released 82 birds, representing 16 species; A juvenile blackpoll warbler is held after being banded and recorded; Rimmer takes a blood sample from a Bicknell’s thrush.

  • Volunteer Liz Lackey takes notes as Vermont Center for Ecostudies biologists, from right, Kent McFarland, Steve Faccio and Sara Zahendra examine a bird. In addition to banding the birds to track their locations, the scientists weigh them, take leg, wing and tail measurements, estimate the age, establish the sex and check for parasites. Zahendra wore a tiara for her birthday.

  • “If I was trapped in a net, I’d be freaking out,” said ornithologist Jason Hill of the Vermont Center for Ecostudies, while working on Mount Mansfield in Underhill, Vt. “Like, is this guy going to help me? Is this predator going to help me?” Hill estimates that he has removed about 5,000 birds from mist nets, a delicate skill that requires certification through the Fish and Wildlife Department. “You still get some that are horribly tangled,” he said. Valley News photographs — James M. Patterson

Valley News Staff Writer
Saturday, September 26, 2015
If you hold in your palm two quarters and a dime you are approximating the weight of the blackpoll warbler, a bird of the northern boreal forest that, on its autumn migration, flies non-stop from northeastern North America over open ocean to the Greater Antilles in the Caribbean and the coasts of Venezuela and Colombia, a staggering distance of between 1,410 and 1,720 miles.

Scientists were reasonably confident that the warbler, a mere 12 grams, flew for about 72 hours over the Atlantic in a remarkable feat of navigation. But they didn’t have the proof.

But when scientists devised a way to track blackpoll warblers during fall migration, banding and outfitting them with miniature, lightweight geo-locators, which the birds wore like tiny backpacks, they were able to estimate their positions during migration as well as pinpoint them at either end of their range.

This was confirmation that the fall migration of the bl ackpoll warbler is one of the longest such recorded flights for a songbird. It is the only warbler known to make such an over-ocean flight.

After scientists from the U.S. and Canada published their findings in the journal Biology Letters in April, it spurred a flurry of global interest. The bl ackpoll warbler became an international avian celebrity, with articles appearing in the Washington Post , Globe and Mail , Japan Times , New York Times and coverage on the PBS Newshour and Vermont’s WCAX-TV.

On a recent morning on Vermont’s Mount Mansfield , a blackpoll warbler caught upside down in a net is less celebrity, and more a small, unassuming ball of black, gray and white feathers. Chris Rimmer, the executive director of the Vermont Center for Ecostudies in Norwich, handles the warbler delicately as he disentangles it from the net. The warbler does not protest.

Rimmer said it looks like a younger blackpoll. “My guess is, it’s a migrant.”

The night before, biologists from the Vermont Center for Ecostudies erected more than 20 mist nets on trails along the mountain’s ridgeline. The lightweight, nearly invisible, finely-meshed nets, which are strung up between poles along foot trails, trap birds without injuring them. The VCE biologists then place them in cotton bags that protect them and keep them from flying away before they can be examined and tagged.

Since the early 1990s, biologists from VCE have annually monitored both forest birds and montane (mountain) forest birds, among other projects, at 168 sites in New England and New York. The purpose is to monitor the health of bird populations, and to see whether, and how, their migration and breeding patterns have altered because of both habitat and climate change.

“There’s a lot of good science going on on this mountain,” Rimmer said.

At 4,393 feet, Mount Mansfield is the highest point in Vermont, with a distinctive profile that resembles a human face gazing skyward. It is also one of the key monitoring sites in the VCE network.

The ridge line is known for its alpine tundra, and for the density of its mixed hardwood forests that support a breeding population of the Bicknell’s thrush, a rare songbird that summers on Mount Mansfield and other balsam fir forests in the Northeast and southern Canada.

Its population, estimated at around 100,000, is under threat from such sources as recreational development, climate change and more localized development of telecommunications towers and wind turbines, according to VCE publications.

The banding station at the top of the toll road on Mount Mansfield’s ridge line, near the “nose,” isn’t really formalized in the sense of having a building to work in. The biologists from VCE set up tables where they weigh, measure and band the birds. They take blood so they can measure mercury levels. They also determine the sex of each bird and photograph them before releasing them. And they record all the data.

Members of Mountain Birdwatch, a VCE bird-monitoring project staffed by volunteers, are also on hand to do field work. “It’s a small group of such passionate people,” said Pat von Trapp, a volunteer and birder.

The expectation was that the nets would catch a variety of birds, but that the biologists would probably see in particular the Bicknell’s thrush, and the blackpoll warbler, which is abundant in the boreal forests of Canada, but is experiencing a decline in New England for reasons that are still unknown.

The population of the blackpoll warbler is estimated at 60 million, according to the American Bird Conservancy website, and its conservation status is listed as one of “least concern” on the Cornell Lab of Ornithology website.

Nonetheless, the population of the warbler has been decreasing by about 6 percent annually across its range , said Bill DeLuca, lead author of the article published in Biology Letters and a research fellow in the Department of Environmental Conservation at the University of Massachusetts, Amherst. No one can pinpoint why.

Because the northern boreal forests in Canada are not currently experiencing any unusual or intense threats to their overall health, DeLuca said, the speculation is that something may be affecting the warbler during migration or where it winters over in the Caribbean and South America.

The hope is that with the information gathered during fall migration and at the northern and southern ends of its range, scientists can begin to understand what is leading to the bird’s decline. (The warblers don’t take the same over-ocean route in spring, DeLuca wrote in an email, because the wind conditions aren’t as favorable to make the trip north over open ocean.)

“It’s the first step with figuring out what’s going on with the species,” DeLuca said. “Now that we have an understanding that Hispaniola and Puerto Rico are important stops — they’re landing there; they’re exhausted — let’s make sure they have the habitat, and have what they need, when they land after a three-day flight.”

Why the warblers undertake such a perilous journey is hard to answer, DeLuca said. “The short answer is because migration in general, over land or water, is when they see highest mortality. Regardless of where (migration takes place), it makes sense to get it over with as quickly as possible.”

DeLuca is also a longtime collaborator with VCE, and he’s one of the biologists who gets up before dawn on Mount Mansfield to begin the inventory. It’s the last time they’ll be on the mountain until next spring to do another count.

The morning is hazy and warm, and through the scrubby, windswept conifers and hardwoods on the ridge you can hear the calls of thrushes, warblers, sparrows and juncos. The vegetation along the ridgeline trails is thick with goldenrod, aster, red bunchberry, white and blue cohosh, with their blue berries, and white baneberry, with its distinctive white berries, or “doll’s eyes.”

There’s an occasional mountain ash, sporting its late summer display of brilliant orange berries. The trails are perpetually slippery because of the seepage from the rock ledges, and thick mosses crowd the trails’ edges. From the western slope there’s a view over to Lake Champlain and Burlington. It is possible in certain locations that the only sounds you will hear are bird calls and gusts of wind — nothing else.

The blackpoll warbler’s call is high and thin, easy to miss unless you are listening for it or are alerted to it. A volunteer with VCE likens it to the sawing sound of an insect, perhaps a cricket or katydid, only softer and less insistent. The song of the Bicknell’s thrush, on the other hand, “is much more elaborate and musical,” said Rimmer.

This morning Bicknell’s thrushes are showing up in the nets with the frequency of commuters going through Grand Central Station. They submit docilely to examination, not protesting when the biologists blow on their chest feathers to see whether they are building up the levels of subcutaneous fat they’ll need to migrate long distances.

The biologists are careful not to overstress the birds during examination. This morning, because the chill of the morning has given way to bright warm weather, DeLuca said, they aren’t as concerned: “If it was colder, you have to be really careful, they’d use up their fat reserves more quickly.”

When the exams are done, the Bicknell’s thrushes sit calmly for a few minutes on the upturned palms of visitors, without showing any fear or urgency to fly away.

Because the biologists at VCE have been studying the Bicknell’s thrush on Mount Mansfield for 15 years, they are used to seeing banded birds return year after year. Rimmer said the oldest Bicknell’s thrush they saw was 11 years old, which is about six years older than the bird’s average life span. There have been three Bicknell’s thrushes, Rimmer said, that they have captured in both Vermont and the Dominican Republic.

“To catch them at both ends of their ranges is unprecedented,” Rimmer said.

Also showing up in the mist nets this morning are beautiful black-throated blue warblers, their caps a gleaming midnight blue; numerous yellow-rumped warblers; white-throated sparrows, which squeak angrily and peck at the fingers of some of the biologists; juncos; a Swainson’s thrush; ruby-crowned and golden-crowned kinglets; and a brown creeper.

Such monitoring efforts, done in collaboration with citizen-scientists, are critical, said Rimmer and DeLuca, because they can engage people in the ir environment. The Bicknell’s thrush and blackpoll warbler aren’t what environmentalists call “charismatic mega-fauna,” the polar bears, panda bears, Siberian tigers or Cecil the lion that tend to draw public attention and adoration.

Still, DeLuca said, the international attention paid to the migration of the blackpoll warbler “ is a pretty special thing. A simple little thing like that may have had more (public) impact than other scientific studies.”

For information on the Vermont Center for Ecostudies, and its work on forest and mountain forest birds, go to http://vtecostudies.org.

Nicola Smith can be reached at nsmith@vnews.com.