For more than 50 years, scientists had tantalizing clues suggesting that Blackpoll Warbler departs each fall from New England and eastern Canada and migrates nonstop in a direct line over the Atlantic Ocean toward South America. The species is spotted only rarely in southern states in the fall, for example, and it has landed on ships in the Atlantic. Plus, radar studies off the tip of Nova Scotia show birds heading south.
Now, for the first time, biologists report “irrefutable evidence” that Blackpolls complete the marathon flight, ranging from 1,410 to 1,721 miles (2,270 to 2,770 km), in just two to three days. They make landfall in Puerto Rico, Cuba, and the islands known as the Greater Antilles, and then go on to northern Venezuela and Colombia.
The researchers, led by Bill DeLuca, an environmental conservation research fellow at the University of Massachusetts Amherst, attached light-level geolocators to 20 birds in Vermont and 20 more in Nova Scotia. They were able to recapture three birds from the Vermont group and two from the Nova Scotia group and analyze the data from their geolocators. They describe their findings in the current issue of Biology Letters.
“We’re really excited to report that this is one of the longest nonstop overwater flights ever recorded for a songbird,” says DeLuca. “It finally confirms what has long been believed to be one of the most extraordinary migratory feats on the planet.”
While albatrosses, sandpipers, and other birds are known for transoceanic flights, the Blackpoll Warbler is a forest dweller that migrates where few of its relatives dare to travel. Most migratory songbirds that winter in South America take a less risky, continental route south through Mexico and Central America. A water landing would be fatal to a warbler.
To prepare for the flight, the birds build up their fat stores, explains Ryan Norris of the University of Guelph. “They eat as much as possible, in some cases doubling their body mass in fat so they can fly without needing food or water,” says Norris. “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.”
Chris Rimmer, executive director of the Vermont Center for Ecostudies notes, “We’ve only sampled a tiny part of their breeding range. We don’t know what birds from Alaska do, for example. This may be one of the most abundant warblers in North America, but little is known about its distribution or ecology on the wintering grounds in Venezuela and the Amazon.”
As for why the Blackpoll flies such a perilous journey while other species follow a longer but safer coastal route, the authors say that because migration is the most challenging part of a songbird’s year, it may make sense to get it over with as quickly as possible. However, this and other questions remain to be studied.