Tiny songbird tracked across vast swaths of open ocean

MONTPELIER, Vermont — A tiny songbird that summers in the forests of northern North America has been tracked on a 1,700-mile (2,735-kilometer), over-the-ocean journey from the northeastern United States and eastern Canada to the Caribbean as part of their winter migration to South America, according to a new study.

Scientists had long suspected that the blackpoll warbler had made its journey to the Caribbean over the ocean, but the study that began in the summer of 2013 when scientists attached tracking devices to the birds was the first time that the flight has been proven, according to results published Wednesday in the United Kingdom in the journal Biology Letters.

"It is such a spectacular, astounding feat that this half-an-ounce bird can make what is obviously a perilous, highly risky journey over the open ocean," said Chris Rimmer of the Vermont Center for Ecostudies, one of the authors.

The warblers, known to bulk up by eating insects near their coastal departure points before heading south, are common in parts of North America, but their numbers have been declining. "Now maybe that will help us focus attention on what could be driving these declines," Rimmer said.

Knowing how the blackpoll warblers migrate helps scientists know more about the implications of changing climate, said Andrew Farnsworth, a research associate at the Cornell Lab of Ornithology who specializes in migration biology and was not involved in the study.

"What happens if birds aren't able to fuel sufficiently to make this kind of flight because of habitat fragmentation and habitat loss in New England or the Canadian Maritimes?" Farnsworth said. "How much energy do they need and if they don't get it, what happens?"

A number of bird species fly long distances over water, but the warbler is different because it's a forest dweller. Most other birds that winter in South America fly through Mexico and Central America.

In the summer of 2013, scientists tagged 19 blackpolls on Vermont's Mount Mansfield and 18 in two locations in Nova Scotia. Of those, three were recaptured in Vermont with the tracking device attached and two in Nova Scotia.

Four warblers, including two tagged in Vermont, departed between Sept. 25 and Oct. 21 and flew directly to the islands of Hispaniola or Puerto Rico in flights ranging from 49 to 73 hours. A fifth bird departed Cape Hatteras, North Carolina, and flew nearly 1,000 miles (1,600 kilometers) before landing in the Turks and Caicos before continuing on to South America.

On their return journeys north, the birds flew along the coast.