Lightweight Songbirds Go Where the Wind Takes Them During Migration

Millions of tiny songbirds - weighing in at less than an ounce - migrate thousands of miles from the US to Central and South America each year on the coattails of nature's wind patterns, according to a new paper published in Journal of Biogeography. 

Scientists long assumed that songbirds simply followed the same "flyaways" that birds and geese used during migration, such as those along each coast, the one up the Mississippi River valley, and the one in the center of the continent.

Most of what we've known about migration routes comes from ducks and geese," lead author Frank La Sorte, a Cornell Lab of Ornithology research associate, said in a statement. "But terrestrial birds are much smaller and they aren't reliant on the same kinds of habitats. There really isn't a narrow migration path for them, and they aren't necessarily in the same place in spring and fall."

Duck and geese flyaway routes were found via tracking the birds and hunting records, methods that do not work for the tiny songbird.

To learn more about the evasive bird, researchers analyzed thousands of sightings to develop a collective picture of where each of the 93 species is during spring and fall migration. They tracked whole groups of songbirds rather than observing them individually, which still painted an accurate picture. They also compared migration routes with seasonal patterns of prevailing winds at night.

"All these species migrate at night, at high altitudes, where we can't see them," La Sorte commented.

What they realized was that songbirds do not just stick to one route when migrating, but rather have a broader range of paths they can take that span out across the continent - in part due to the fact that they aren't tied to a single habitat.

Also, these birds demonstrate their intelligence by taking advantage of stronger tailwinds in spring and less severe headwinds in fall, using up less calories and energy.