Maine’s Songbird Highway

Scientists aim to unravel the mysteries of migration in the Gulf of Maine.

By Kim Ridley
Reader photo submitted by eswanson

The morning air smells of balsam and wet duff as Adrienne Leppold sets out on a narrow trail to check the mist nets she set up before dawn to capture birds in a patch of forest in Orono. A great-crested flycatcher cries “wheep, WHEEP,” one of a dozen or so species calling and singing in the trees.  Leppold doesn’t pause, however, to scan the branches. She makes a beeline for the ne ts, followed by three students she’s teaching the precise and delicate art of banding birds.

A common yellowthroat, a hermit thrush, and an ovenbird dangle like snagged leaves in the first set of nets. Leppold immediately starts extricating them. “It’s sort of like taking a t-shirt off a little kid,” she explains as she deftly untangles the yellowthroat in a matter of seconds. “You have to lift the net up over his head.” Leppold briefly holds the bird up for the students to admire its yellow and olive green plumage and jaunty black mask, and then gently pops it into a brown paper lunch bag.

Back at the banding tent, Leppold examines, measures, and weighs the birds, and attaches a tiny aluminum identification band to each bird’s leg, working with the efficiency and ease of someone who has done this many times. She calls out data for the students to log and patiently shows them how to handle the birds and release them. This is a slow morning for Leppold, who has banded upwards of 100,000 birds over the past decade and is now studying songbird migration in the Gulf of Maine as a PhD student in Dr.  Rebecca Holberton’s Lab of Avian Biology at the University of Maine.

The pace today is a far cry from the wild scene Leppold and Holberton encountered in 2009 on Metinic Island in Penobscot Bay, where Leppold had set up a new banding station for the Maine Coastal Islands National Wildlife Refuge — and soon made a stunning discovery. Leppold was working in the banding tent on a bright October morning when Holberton called her outside. To their astonishment, hundreds of warblers and other migrating songbirds covered the ground, and hundreds more streamed over the island from the east.

“I remember watching a flock of about 150 yellow-rumped warblers that kept hovering and circling over the island,” recalls Leppold, who is in her early thirties and wears her long, curly red hair in a braid. “Then about half of them kept going and the other half came down into the trees. It was almost like I could feel them thinking.”

The spectacle Holberton and Leppold witnessed wasn’t just a fluke. That fall, banding crews on Metinic and several other Maine refuge islands captured more than 5,500 birds representing seventy-five species — far more than had ever been found at any other banding station in the Northeast. Based on similarly huge numbers over the next two years, Leppold has discovered that the Gulf of Maine is a “superhighway” for songbirds migrating between Canada and wintering grounds as far away as South America. She and Holberton estimate that between 250,000 and 500,000 songbirds fly through the region every autumn. Maine’s coast and islands, they say, provide these birds with crucial “stopover” habitat, places where they can rest, feed, and regroup during the most dangerous time in their lives.

“More than 80 percent of bird mortality happens during migration, and some of these birds are already in steep decline,” Leppold says. “We’re finding that stopover habitat on islands like Metinic provide critical opportunities for songbirds to reorient themselves during migration and still get to where they need to go.”

Leppold is documenting how migrating songbirds use Maine’s islands and coast, which is part of a larger effort to identify important areas of stopover habitat to protect in the Gulf of Maine, as well as the flyways that connect them. She and Holberton are among more than two-dozen researchers in the U.S. and Canada working together through the Northeast Regional Migration Monitoring Network to better understand bird and bat migration in the Gulf of Maine. At a time when new pressures are emerging along the Maine coast, including the race to develop coastal and offshore wind power, the network’s findings will help agencies and communities make more informed decisions about wind energy projects, land development, and conservation.

“The Gulf of Maine is an important crossroads for birds, especially during fall migration,” says network member and biologist Trevor Lloyd-Evans, banding director at the Manomet Center for Conservation Sciences, who has been studying migration in the region for more than forty years. “The more we know about the significant locations birds are using within the region, the better we can inform the debate on future turbine siting to avoid, or at least minimize, impacts to birds and other wildlife.”

Hundreds of thousands of songbirds, as well as waterfowl, seabirds, shorebirds, and raptors, spend at least part of the year in the Gulf of Maine. Tracking avian comings and goings in a region that encompasses 36,000 square miles of ocean and more than 7,500 miles of coastline from Nova Scotia to Cape Cod, not to mention Maine’s 4,600-plus islands, is no small task. But network researchers are combining time-honored techniques such as banding with newer technologies to get a clearer picture of when and where birds are traveling through the region.

Songbirds are particularly tricky to track because most of them migrate at night, but many species utter short, distinctive flight calls believed to help them communicate with each other in the dark. Holberton’s lab is using acoustic monitoring to eavesdrop on these nocturnal conversations. Her team is recording and analyzing thousands of these flight calls to glean new clues about who these birds are, and are correlating that information with radar and banding studies to zero in on where and when they’re migrating along the Maine coast.

In addition to figuring out where these birds are flying and who they are, Holberton and her colleagues are also sleuthing out where they’ve been. Analyses of stable isotopes in blood and feather samples have revealed that some birds coming through the Gulf of Maine have migrated from as far away as Alaska and western Canada.

“More than 80 percent of the songbirds that come through our area are boreal and Arctic songbirds whose ecosystems are getting hit the hardest with climate change,” Holberton says. “Many of the boreal species we have coming through are declining globally, like the Bicknell’s thrush and the blackpoll warbler, which is the fastest declining warbler in North America,” she says, noting that blackpoll numbers have dropped by more than 90 percent in the last decade.

Leppold says the fact that blackpolls, Bicknell’s thrushes, and other beleaguered species migrate through the Gulf of Maine underscores the importance of places such as Metinic Island that provide stopover habitat. “Our studies are showing that some of these species are critically dependent on this region during migration to sustain their populations,” she says.

Bird scientists classify stopover habitat into three categories: fire escapes, convenience stores, and five-star hotels. Fire escapes are merely places to land, such as a ledge or structure. Convenience stores offer some shelter and food, and five-star hotels afford abundant shelter and food. Birds generally spend a day or less on a fire escape, up to three days at a convenience store, and upwards of a week at a five-star hotel, where they can rest and tank up to replenish fat reserves for their long journeys.

“Metinic is a big-time convenience store,” Leppold says. “I’ve told students that I get tired when I drive a lot at night, and if it weren’t for convenience stores I would have ended up in a ditch somewhere.”

For birds, finding convenience store habitats can literally be a lifesaver, observes Leppold. More than 80 percent of songbirds migrating in the fall are “hatch year” birds that are making the journey south for the first time. While their genetic compass guides them south, strong winds and storms can blow them off course until they drift east out over the ocean.

Earlier studies have suggested that many songbirds that turn up along the Gulf of Maine are in poor condition and likely to perish, but research by Leppold and other network scientists is challenging that assumption. Based on data on more than 12,000 birds banded on Metinic and other coastal refuge lands, Leppold is finding that many of these birds are in good shape and are either using Gulf of Maine islands and coastal areas to reorient themselves or deliberately island- and peninsula-hopping across the gulf from Nova Scotia.

Leppold and Holberton are also collaborating with network colleagues, including Dr. Phil Taylor, biology professor at Acadia University in Nova Scotia, to track the movements of individual songbirds using radiotelemetry. These and other studies will yield further clues about the most important stopover habitat to protect, as well as other insights into how to help shore-up the future of tens of thousands of birds traveling through the Gulf of Maine, which is one of the richest ecosystems on earth.

“I think we need to stop once in a while and really take in where we live,” Holberton says.

“The Gulf of Maine is an important migratory conduit for these birds, and I think that makes us have even more responsibility to protect this region.”