At the same time, the scientists performed an identical experiment with another population of northern wheatears that spends summers on Baffin Island in Arctic Canada. The one bird whose geolocator they were able to recover on Baffin Island spent its winter in Mauritania, in western Africa. That bird traveled southeast on its fall journey to Africa, starting its trip with a 2,000-mile Atlantic Ocean crossing, from Baffin Island to the British Isles.
The Alaska and Baffin Island populations of wheatears probably never meet, either on the tundra or on the savanna. The scientists determined this by examining their feathers using isotope analysis, to determine the water sources from which the birds drank.
Scientists don’t know for sure how the two groups of wheatears developed those parallel life strategies on different halves of the globe. Bairlein said that during the last great glacial period, in which much of the far north was ice-covered, wheatears may have been holed up in the Middle East. When the glaciers shrank from the continents, one group of wheatears may have expanded to the northeast, reaching Alaska, while the other drifted northwest, reaching Canada via Europe and Greenland. Somehow, they lost touch.
Another German scientist in 2010 studied the wheatears now staging in Wales, Alaska. Heiko Schmaljohann, also of the Institute of Avian Research, attracted Wales wheatears to electronic scales holding plastic dishes full of mealworms. When a bird landed, he and his helpers looked through a spotting scope to record its weight. The scientists wanted to find how fueled-up the birds were before they headed out over the Bering Strait.
Schmaljohann captured more than 100 wheatears — all of them, new birds that hatched that summer — and fitted many with radio transmitters. He found that most birds took off just after midnight on August nights, and almost all in a southwest direction from Wales.
How do birds that pecked from eggshells on Alaska tundra just this summer know how to make it to Africa? The birds are born with that knowledge, maybe tied to the Earth’s magnetic field and geographic landforms.
Why do wheatears and other migrating birds wait until night to fly? That’s a tough one to answer, but researchers think the cover of darkness might protect birds from predators. Cooler temperatures and more stable flying conditions might also exist at night, and, if birds land during daylight, insects are easier to find.
The northern wheatears that knife into the wind at Wales and leave Alaska will not reach Africa until November. After four months in the sub-Sahara with giraffes, they will again feel the urge and hop from an acacia tree branch. Their return trip to Alaska in 2020 via the same route will be several weeks faster than their fall journey. The nomads will then raise new wheatears with the help of Alaska’s most abundant natural resource, bugs.
Since the late 1970s, the University of Alaska Fairbanks’ Geophysical Institute has provided this column free in cooperation with the UAF research community. Ned Rozell is a science writer for the Geophysical Institute.