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Study: For migrating Northern Wheatears and Blackpoll Warblers, success is blowing in the wind

Northern Wheatear, Whiteworks, Dartmoor, Devon, England, by Aviceda (Wikimedia Commons).
Northern Wheatear, Whiteworks, Dartmoor, Devon, England, by Aviceda (Wikimedia Commons).

Northern Wheatear is the only songbird that breeds in northern North America and spends its winters in sub-Saharan Africa. Each fall, it migrates either westward across all of Asia or eastward across the Atlantic Ocean.

See photos of Northern Wheatear.

Since the distance from Greenland and northeastern Canada to northwestern Africa is about 4,000-5,000 kilometers (2,485-3,100 miles) and entirely over water, it’s assumed that most eastbound wheatears fly to Europe first and then continue south. And observations by birders support this: In spring and autumn, they record the species on the west coast of Europe, even east of Britain, regularly.

But wheatears also show up regularly on islands off of Africa, including Selvagem Grande, an islet off Morocco. Their arrival raises the possibility that favorable winds might enable the bird to cross the ocean in one hop.

Curious about the feasibility and reliability of such a flight, researchers from the Institute of Avian Research in Germany and the University of Amsterdam took three decades of autumnal wind data and built a model to test how wind conditions, altitude, and the amount of fat a wheatear carries would affect its journeys.

“For modeled individuals with high fuel loads, flying at altitudes of about 3,000 meters [9,800 feet], successful nonstop trans-Atlantic flights reached Africa on 62 percent of departure days,” write the researchers. The flights depended on favorable tail winds and lasted less than three days, 31-68 hours.

“Given the arrival success in the present study, we conclude that migrating 4,000 km nonstop across the North Atlantic Ocean in autumn may be a feasible migration strategy for wheatears of Canadian origin.”

Moreover, say the authors, the assumptions built into their model were conservative. “This implies that similar or even longer nonstop migration by landbird migrants may be feasible, including nonstop flights of 3,250-4,000 kilometers [2,019-2,485 miles] by Blackpoll Warblers to South America from eastern North America.”

Read the abstract

Marc Bulte, James D. McLaren, Franz Bairlein, Willem Bouten, Heiko Schmaljohann, and Judy Shamoun-Baranes (2014) Can wheatears weather the Atlantic? Modeling nonstop trans-Atlantic flights of a small migratory songbird. The Auk: Ornithological Advances 131: 363–370. Abstract.

A version of this article appeared in the October 2014 issue of BirdWatching magazine. Subscribe.

 

Originally Published

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