“At every moment of every day, morning or midnight regardless of the season, there are birds aloft in the skies of the Western Hemisphere, migrating.”  — Scott Weidensaul

Each September for millennia, triggered by decreasing daylight, most North American nesting birds begin their migration south. Each day last week at dusk flocks of southbound Canada geese honked over my home. There is one small nondescript looking bird though that escapes our ears and eyes. The blackpoll warbler has a relatively mundane name but its migration south is truly extraordinary. In fact, its flight from Maine to South America is otherworldly, a rare example of science being more unbelievable than science fiction. 

From their breeding grounds in Canada’s vast spruce-fir forest, blackpolls first fly east each September to converge on Sherman’s Point, Beauchamp Point, and other coastal Maine peninsulas and islands. For Alaskan blackpolls, their late summer arrival in Maine is a 3,000-mile dogleg flight before September’s northwest winds triggers the next leg of their journey towards the equator. 

In Acadia National Park many years ago, I plucked a fall migrant blackpoll warbler from in a mist net - a badminton-like net - designed to temporarily capture birds for banding studies. The bird was smaller than a chickadee and it weighed less than my ballpoint pen used to record data. Blowing softly on the bird’s dense breast feathers revealed the secret to its non-stop trans-oceanic flight. At the base of its feathers, tucked beneath transparent skin, were yellow globs of fat. The fat deposits function as jet fuel, propelling the blackpoll’s 72 - 88 hour flight to Venezuela, a distance of 2,300 miles from mid-coast Maine. By the time it reaches South America, the bird will have lost 25 per cent of its weight. An avian physiologist studying blackpolls likened the bird’s long-distance flight to the medical equivalent of a 160 lb. marathon runner averaging 4-minute miles for 70 hours, and losing 40 lbs.

Blackpolls feed primarily on insects during the summer breeding season. Like runners before a September marathon, blackpolls reduce their protein intake by instead consuming large quantities of fruits high in fats, carbohydrates and antioxidants. They’ve mastered the practice of carbohydrate loading by eating bayberries, Viburnum fruits, and nectar. A backyard birder once sent me a photo of a September blackpoll drinking from a hummingbird feeder while a hovering hummingbird waited to feed.   

Blackpolls prepare for their remarkable flight by doubling their body mass by gorging on coastal berries and seeds. Similar to airplanes stuck on runways during inclement weather, blackpolls remain grounded until a wet weather low front clears. In Maine, autumn high fronts are usually associated with strong northwesterly winds. This benefits blackpolls because tailwinds help them conserve energy. They’ll need all the help they can get from the weather gods. For reasons that are not entirely understood, in late September blackpolls begin their trans-oceanic flights south from Maine after sunset. Some biologists speculate it’s to avoid the gauntlet of hungry migrating forest hawks. Others suspect it’s to use the North Star as a navigation aid or too minimize their exposure to the sun’s warmth. What is known though is that strong northwesterly winds sweeping across Maine’s coastline carries birds far out to sea in a southeasterly direction.  For the next 40 – 50 hours, the diminutive birds will fly over the Atlantic, climbing to a height of 5,000 feet, on wings humming at twenty flaps per second. Having flown all night and most of day two, blackpolls catch the one break they need. Trade winds.  Somewhere around Bermuda, island meteorologists report seeing the birds on radar screens. The warblers glow as little, moving green specks. At a radar ornithology lab at Clemson University in South Carolina, Dr. Sidney Gauthreaux monitors the blackpoll’s migration on a set of screens.

According to Scott Weidensaul, author of Living on the Wind: Across the Hemisphere with Migratory Birds: “The warblers follow a curving track, steered and abetted by the Trade Winds. The tiny birds are shepherded back toward South America, finally making landfall along the coast of Venezuela or Guyana, an over-water trip of about 2,000 miles – a passage with no rest, no refueling, no water, during which each will have flapped its wings nearly three million times.”

For the lucky ones making landfall after an arduous non-stop flight, they will rest and feed for several days in northern South America. Many blackpolls will then continue their journey south to spend the winter in the Amazon Basin of Brazil. Some birds, especially under weight ones, fall from the sky to their deaths in the Atlantic. 

In late September, step outside on a crisp starry night and listen for the high-pitched calls of migrating songbirds overhead. Blackpoll warblers will be making some of those calls. Their migration is the longest of any North American songbird, an annual round trip of eleven to twelve thousand miles. The little bird with big ambitions and a bigger heart is going places.

Ron Joseph of Camden is a retired Maine wildlife biologist.

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