By Wesley Hochachka
Which species of North American songbird is widespread enough that it’s found on both eastern and western sides of the continent but is still a rare treat for most birdwatchers? And proportional to its body size, which songbird regularly migrates farther than the globe-trotting Arctic Tern? The answer is: Northern Wheatear, the only North American representative of a widespread Old World genus in the thrush family.
Northern Wheatears breed all the way across northern Eurasia and reach North America in both the west (Alaska and the Yukon) and the east (the Canadian Arctic). So why don’t we get to see them in the winter, the way we get to see Snow Buntings, American Tree Sparrows, and Snowy Owls? Because all of the world’s Northern Wheatears, save a few vagrants, spend the winter in the same region: sub-Saharan Africa.
Not only that, but they take radically different routes to get to Africa, according to recent research presented by Franz Bairlein, director of Germany’s Institute of Avian Research. Bairlein unfolded the Northern Wheatear’s story for a global audience of ornithologists at the International Ornithological Congress in Tokyo, in August. His team used tiny, lightweight geolocator tags to follow wheatears traveling from either side of the North American arctic to their wintering grounds, providing the first hard proof of the long-suspected migration routes of these birds.
The routes could scarcely have been more different. From the eastern arctic of Canada, Wheatears traveled through Greenland to northwestern Europe before flying south to western Africa. Their western arctic compatriots went the other way around the globe: they flew westward to Siberia and then diagonally across Asia to wind up in eastern Africa. The migration distances are astonishing, particularly the Alaskan birds’ journeys, which added up to roughly 15,000 km. Wheatears from the eastern Canadian arctic traveled a mere 7,500 km, although the first leg of their journey was a 3,500 km trans-Atlantic crossing to Europe with only one possible resting point, Greenland, en route.
The time that wheatears spend on these migrations was what I found most surprising: birds traveling across Asia took roughly 3 months to reach Africa and two and a half months to return to North America. That’s comparable to the roughly 3 months that North America’s wheatears spend on their nesting grounds, and is only marginally less than they spend on their wintering grounds (4 or 5 months for western and eastern American arctic, respectively). These birds were spending so little time in any one location that, if they were humans, they possibly would not be considered legal residents of any nation on earth!
The discovery of these travel itineraries has allowed Bairlein’s research group to explore other aspects of migration. Because the two populations of wheatears cross such different types of terrain, the researchers were able to learn about how songbirds in general adapt to the environments that they cross during long-distance travel. Bairlein’s group specifically contrasted the long transoceanic flights of wheatears going east to Europe against the largely overland routes of western arctic birds. And these two populations do prepare for migration differently. Eastern North America’s wheatears fatten massively, approaching double their normal body weight prior to their ocean crossings, whereas western wheatears accumulate far less fat for their journeys. Again, if these birds were human, the rate and extent of fattening, and the physiological processes underlying them, literally would result in these birds being classified as dangerously obese and with type 2 diabetes!
Bairlein’s group also found that these physiological differences are genetically hard-wired into the birds, as are the directions that they navigate. If you were to take the egg from an Alaskan wheatear and transplant it to Baffin Island in the eastern Canadian arctic, the resultant offspring would travel in the wrong direction, westward across North America. Even if such a transplanted bird did head eastward across the Atlantic, its body would still be preparing for a “western” migration and wouldn’t store up enough fuel reserves to reach Europe.
What impressed me the most about Bairlein’s presentation is the way that he applied his knowledge of natural history to select a great study species even though it is not one of the “classic” species of birds for an ornithologist to study. Examples of classic species include Tree Swallows and bluebirds (North America) and Great Tits and Blue Tits (Europe). These birds are easily studied because they live close to researchers and nest in boxes—and scientists have learned a great deal from them. But by starting with this unusual yet inspired choice of study species, Bairlein’s research has shed new light on the ways that migratory birds, and in particular long-distance migrants like Red Knots, Hudsonian Godwits, and Blackpoll Warblers, are adapted to make their great migratory journeys.
More about migration:
- Take the Long Way Home: “Green Wave” Explains Bird Migration Routes
- These 8 Unexpected Migration Routes Give You Reason to Go Birding in Summer
- Flyways for Flyweights: Small Birds Capitalize on Weather Patterns During Epic Migrations
- ID Workshop: Use 4 Basic Keys Plus Migration Timing to Sort Out Your Thrushes
(Wesley Hochachka is the assistant director of Bird Population Studies at the Cornell Lab of Ornithology. Top image: Adult male Northern Wheatear in breeding plumage, Alaska, by Mark Peck. Images on map: Northern Wheatear in in Canada by wayne.geater, and in Alaska by Billy Lindblom. All images shared via Birdshare.)