The northern wheatear, Oenanthe oenanthe, weighing in at an ounce or less, was known to have one of the largest breeding ranges for a songbird—stretching from eastern Canada across Greenland and Eurasia to Alaska— but up to now, researchers had been unable to establish where the birds that summered in Canada and Alaska spent the winter.
Equipping forty-six birds with super-lightweight sensors called geolocators, which recorded light intensity during the time of deployment, a team including Franz Bairlein and Heiko Schmaljohann of the Institute of Avian Research in Wilhelmshaven, Germany, followed two wheatear populations as they left from Alaska and the eastern Canadian Arctic. Based on times of sunset and sunrise, as well as on the length of the night-and-day migrations, the team could estimate the birds’ routes in the fall and in the spring. Although the team recovered only four of the geolocators, those supplied plenty of data with which to reconstruct their respective carriers’ geographic locations over time.
The researchers also analyzed chemical signatures in some wheatears’ feathers grown the prior winter. The approximate location of the birds when they grew those feathers was gleaned from ratios of stable-hydrogen isotopes, which are distinct to a region’s precipitation, evaporation, and temperature. The data from three Alaskan wheatears showed that in the fall they flew approximately 9,000 miles over Russia, Kazakhstan, and the Arabian Desert to spend the winter in eastern Africa before flying back to Alaska in the spring. On the other hand, the one Canadian wheatear whose geolocator was recovered had spent the winter in western Africa. It traveled about 2,100 miles over the Atlantic, turned south at the United Kingdom, and flew some 2,500 additional miles to reach its winter destination. During those marathon migrations, linking two distant continents,the tiny wheatears flew at speeds averaging between 80 and 180 miles per day. (Biology Letters)