Solving the case of the migratory blackpoll warbler

Guelph prof part of team to learn bird’s perilous route

GUELPH — In the world of science, Ryan Norris and a team of researchers from across North America have solved one of the oldest mysteries about a migratory bird.

By outfitting the blackpoll warbler with tiny tracking devices, scientists have determined that the migratory songbird travels for three days over the Atlantic Ocean when it heads south for winter.

“The blackpoll warbler behaves unlike any other bird,” said Norris, a University of Guelph professor in the department of integrative biology.

“They seem to disappear when they migrate. They are seldom seen south of New England or the Maritimes.”

Norris said for the past 50 years the best science could do was make assumptions that the birds migrated over the ocean. The data the team collected confirms that the birds make a three-day overwater flight.

“Another migration mystery has been solved,” Norris said.

The study also involved researchers at Acadia University in Nova Scotia, Bird Studies Canada, the University of Massachusetts, the Vermont Centre for Ecostudies and the Smithsonian Conservation Biology Institute. It was published this week in the Royal Society journal Biology Letters.

The data confirmed the tiny birds, that weigh about 12 grams, travel from 2,270 to 2,770 kilometres before landing.

Norris said they likely take advantage of trade winds, but still called it “one of the greatest migrations feats of nature.”

“It’s a do or die migration,” he said.

“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, another 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.

Norris said no other birds take this migration route and that raises the question why.

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 1,600 kilometres before landing in the Turks and Caicos before continuing on to South America.

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