You would have learnt in school that migratory birds fly south for the winter and go back north during the summer. Textbooks might even have forced you to learn about the amazing Arctic Tern, a bird that travels 90,000 km round-trip as part of its migration. Yet it's hard to imagine what migration actually looks like, except for noticing a few new birds showing up or disappearing when the weather changes.
Scientists at the Cornell Lab of Orinthology have now taken care of that problem. Using millions of observations from the eBird citizen-science database, scientists documented the migratory patterns of 118 different bird species over an entire year, across the Western Hemisphere.
The result is this mesmerizing map, which maps the average location of the different species over the course of the 12 months.
The results suggest broad overlap with the way a huge number of species migrate, travelling over the Atlantic Ocean during the autumn to spend winter in the Caribbean and South America, and then, in a clockwise loop, returning back to the north in the spring.
“These looped pathways help the birds take advantage of conditions in the atmosphere,” said Frank LaSorte, lead author of the research. “Weaker headwinds and a push from the northeast trade winds as they move farther south make the fall journey a bit easier. The birds take this shorter, more direct route despite the dangers of flying over open-ocean.”
The research gives the scientists a better idea of how different kinds of species travel during their migration. It will also help with conservation efforts, especially for activists working to protect bird populations that travel great distances over the course of the year.