Hold two nickels and a dime in your hand. That's the summer weight of a Blackpoll Warbler. This black-capped songbird nests from the mountain forests of New England across the boreal forest to Alaska and, after an epic migration, spends its winters in South America. This is a bird that only knows one season – summer.
This tiny songbird's fall migration is fueled entirely by stored fat. Scientists have calculated that a Blackpoll Warbler has to weigh more than seven tenths of an ounce to complete a trans-Atlantic flight. For us, the metabolic equivalent would be to run four-minute miles for 80 hours.
Blackpolls are one of the largest warblers, a fact that probably stands them in good stead in their immense overwater flight and on the nesting grounds, where temperatures may dip below freezing well into the breeding season. The male, more strikingly marked-with his black cap (or “poll”) and streaked sides-than the more plain female, sings his high-pitched song from treetops throughout his territory. During June the song is a characteristic feature from the stunted spruce-fir forests that crown higher peaks of the Northeast to the lowland boreal evergreen forests.
Blackpolls build their bulky, well-concealed nest low in a conifer, next to the trunk or, occasionally, at the end of the splay of a conifer branch. Three to 5 creamy buff or greenish eggs, spotted and/or wreathed with brown are laid. Both parents tend the young.
After the breeding season is done and molting is complete, each September they move to the north Atlantic coast. Gorging on insects and berries, they double their weight. Fat bulges from throat to the tail. And then a cold front arrives from the north and they’re gone.
With favorable tailwinds the birds depart into the darkening southeast sky and sail over the vast Atlantic Ocean. Radar data show migrating songbirds fly at an altitude up to 2,600 feet within four hours after sunset in New England, and rise to 6,500 feet by the time they reach Bermuda. As they approach the Tropic of Cancer, the winds shift to the northeast, allowing for drift toward the Lesser Antilles and South America. Over the Lesser Antilles, flight above 13,000 feet results in lower wind speeds and less headwind than at lower altitudes. They have been recorded as high as 20,000 feet over Antigua. As they approach South America over Tobago their altitude drops to just 2,500 feet. It is believed that their entire non-stop flight lasts 80 to 90 hours with an averaging speed of 25 miles per hour, but no one has ever tracked an individual Blackpoll Warbler on its flight.
- If a Blackpoll Warbler were burning gasoline instead of its reserves of body fat on migration, it could boast of getting 720,000 miles to the gallon. A Boeing 747 needs about 10 gallons of fuel to fly one mile and a small Cessna travels just 10 miles per gallon.
- This tiny songbird is fueled entirely by stored fat. Scientists have calculated that a Blackpoll Warbler has to weigh more than seven tenths of an ounce to complete the trans-Atlantic flight. For us the metabolic equivalent would be to run four-minute miles for 80 hours
- One of the highest pitched songs of any bird. Some people can’t hear them.
In the U.S., Blackpoll Warbler populations declined by 7.3 percent per year between 1966 and 2010, resulting in a cumulative decline of 96 percent, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 60 million with 76 percent spending some part of the year in Canada, and 24 percent in the US. The 2014 State of the Birds Report listed the Blackpoll Warbler as a ‘Common Bird in Steep Decline’.
VCE’s Mountain Birdwatch project monitors songbirds that breed in the montane fir and spruce forests of the Northeast, such as Blackpoll Warbler. Our data provide the only region-wide source of population information on these high-elevation breeding birds.