A team of ornithologists led by William DeLuca of the University of Massachusetts, Amherst, reports the first direct evidence that the blackpoll warbler (Setophaga striata) completes an autumn trans-Atlantic migration ranging from 2,270 to 2,770 km (1,410 to 1,721 miles) and requiring 2 to 3 days of non-stop flight.
The blackpoll warbler (Setophaga striata). The ornithologists found that in some cases, the birds flew more than 2,500 km, non-stop, to reach their destinations. Image credit: William H. Majoros / CC BY-SA 3.0.
The blackpoll warbler is a relatively small songbird weighing only 12-13 g. Its wingspan is usually less than 23 cm across.
The species primarily breeds across Alaska and north-central Canada. Smaller numbers breed in southeastern Canada, and isolated breeding populations exist in the mountains of New England and New York.
The bird is a long-distance Neotropical migrant. For more than fifty years, it has been hypothesized that, during autumn migration, blackpoll warblers depart northeastern North America and undertake a non-stop flight to Puerto Rico, the Lesser Antilles, or northern South America. There have been no definitive answers – until now.
“This is the first study to provide direct evidence of the birds’ migration route – we found they flew directly over the Atlantic Ocean to reach their wintering grounds in South America,” said Prof Ryan Norris of the University of Guelph, Ontario, Canada, the senior author of the paper published in the journal Biology Letters.
The team used geo-locators to track blackpoll warblers on their annual flight south to the Caribbean and on their way north to Canada and the United States in the spring.
The 0.5-g devices sat on the backs of the birds and were attached using leg loop harnesses, much like a person would wear a backpack. They were attached to 20 birds in Nova Scotia and 20 more in Vermont in the summer.
The scientists also placed colored plastic bands on the birds to identify them when they returned.
The geo-locators tracked the birds’ flight path, but, because of their small size, they were not able to transmit the data remotely.
“We waited for them to return in the spring and then searched the forest to find the blackpolls with geo-locators,” Mr DeLuca explained.
“When we accessed the locators, we saw the blackpolls’ journey was indeed directly over the Atlantic. The distances traveled ranged from 2,270 to 2,770 km.”
Each bird took 2.5 to 3 days to make the trip.
“To prepare for the flight, the birds build up their fat stores. They eat as much as possible, in some cases doubling their body mass in fat so they can fly without needing food or water,” Prof Norris said.
“For small songbirds, we are only just now beginning to understand the migratory routes that connect temperate breeding grounds to tropical wintering areas,” Mr DeLuca said.
“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.”
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William V. DeLuca et al. Transoceanic migration by a 12 g songbird. Biology Letters, published online April 01, 2015; doi: 10.1098/rsbl.2014.1045
