The blackpoll warbler weighs just half an ounce (12 grams), but the species takes part in a marathon nonstop migration which brings the animals from New England and eastern Canada down to South America.

At the start of each winter, the birds begin a three-day journey over the Atlantic Ocean to spend the winter months on the southern continent. This arduous migration can carry the birds as far as 1,700 miles without sleep, and can take up to three days.  

Blackpoll warblers that were the subject of a new study spend summers in New England and eastern regions of Canada.

Researchers captured 20 of the birds in Vermont, as well as the same number in Nova Scotia. These animals were then fitted with solar geolocators to track and record the motions of the birds. These devices function due to the fact that the time of solar noon varies by longitude, while the length of days is dependent on latitude. By studying these readings, researchers were able to determine where the birds had traveled during their flights. Until recently, the trackers were too large to be carried by the tiny animals. The trackers weigh 0.5 grams (about 0.018 ounce) and are about the size of a dime.

Transatlantic migrations of blackpolls have long been suspected by biologists, as the birds will sometimes rest on ships crossing the ocean. The birds have also been tracked on radar, although this new study was the first to positively document the marathon journey.

Several other species of birds migrate between North America and South America, but most take a far-safer route, flying overland as they cross Mexico and Central America. Blackpolls would perish if they were ever forced to land on the water during the journey.

"For small songbirds, we are only just now beginning to understand the migratory routes that connect temperate breeding grounds to tropical wintering areas. We're really excited to report that this is one of the longest nonstop overwater flights ever recorded for a songbird, and finally confirms what has long been believed to be one of the most extraordinary migratory feats on the planet," Bill DeLuca of the University of Massachusetts Amherst said.

Researchers recovered geolocators from two of the birds originally seen in Canada, as well as two from the small northern New England state. The tiny birds initially make landfall in Puerto Rico, Cuba and the Greater Antilles islands, and from there head into northern Venezuela and Columbia.

In order to prepare for their journey, the birds consume large amounts of food to build up supplies of fat.

"They eat as much as possible, in some cases doubling their body mass in fat so they can fly without needing food or water. For blackpolls, they don't have the option of failing or coming up a bit short. It's a fly-or-die journey that requires so much energy," Ryan Norris of the University of Guelph in Ontario told the press.

Analysis of the migratory routes of blackpoll warblers was published in the journal Biology Letters.

Photo: Don Faulkner | Flickr

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