Study finds birds that migrate long distances survive better in winter

[Cara J]

Using weather radar to study North American bird migrations, researchers at the Cornell Lab of Ornithology made a surprising discovery: birds leaving the United States on long, hazardous journeys to the tropics each fall actually survive better than those making shorter flights to cooler climes closer by. Of those short-distance migrants, which include American robins (Turdus migratorius), dark-eyed juncos (Junco hyemalis) and many sparrows, “many don’t make it through the winter,” said Adriaan Dokter, a postdoctoral fellow at the Cornell lab and lead author of the study published in Nature Ecology & Evolution. Dokter’s team used data from 143 weather stations across the United States between 2013 and 2017, and cloud computing to crunch all that data. Developing complicated algorithms to measure the amount of bird biomass in the air picked up by the radar, they estimated how many birds cross the borders with Canada and Mexico each year in spring and fall. They found 4.7 billion birds fly south over the southern U.S. border each fall. Another 4 billion birds leave Canada for the United States. Those numbers plunge on the return journeys. In the spring, 3.5 million birds cross back to the United States — a 76 percent [...]

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