Year of the Bird Series: September – Blackpoll Warbler

Article by Rick Ludkin

We begin to see the first Fall Blackpoll Warblers at the beginning of September with their numbers swelling as the month proceeds. This hardy little bird, that spends the Winter in wooded habitats in South America as far south as Bolivia, breeds in the boreal forest anywhere from Newfoundland to Alaska. Its flight south is what captures the imagination.

The bird first makes an overland journey to southern Nova Scotia or the New England States. For some birds this isn’t particularly arduous. But for a bird coming from the Yukon or Alaska it’s a long trek. During this jaunt the bird puts on some fat for energy but not a great deal of it. A “lean” or fat-free bird weighs around 9.5 – 11 grams. The birds during this stage of the journey come in at about 13.5 g. But in the staging area in New England the birds can put on a great deal of fat, sometimes doubling their fat-free weight. This is to fuel a long, non-stop flight of over 80 hours that will take them to the northeast coast of South America!

The fat birds wait until the conditions for migration are right – the movement of a cold front, a high pressure system over the area bringing with it northwest winds, cool temperatures and clear skies. After takeoff they climb until they reach an altitude of between 1,000 and 2,000 meters following a southeast heading. The area of the Northeast Trade Winds provides beneficial following winds but in the proximity of the Lesser Antilles the winds at lower elevations move more to the east and strengthen, becoming something of a hazard. At this point the birds may climb as high as 4,500 meters to find beneficial winds. As they approach the coast of South America they begin their descent and make landfall after a non-stop flight of about 3,500 kilometers!

The Blackpolls we catch and band at Ruthven usually weigh around 12.5 grams; these are birds that are making for New England to fatten. But occasionally we have caught birds weighing more than 20 grams and we ask ourselves whether, with the right conditions, they might start their non-stop flight from here.