Wednesday, November 14, 2018

Speaking of Science: Fly by night

Speaking of Science
Talk nerdy to us

A flock of Canada Geese fly over the reflecting pool at sunset in Washington, D.C. on Jan. 28, 2017. (Jonathan Newton/The Washington Post)

This week, I spoke with Cornell University ecologist Cecilia Nilsson, who studies bird migration using Doppler weather radar. The reason: Most of the birds she studies fly by night. It's tough to spot a sparrow in the dark.

Big, honking flocks of geese heading south for the winter — in broad daylight — give a misleading impression. Seven in 10 bird species in the United States migrate at night, Nilsson said. Many are small birds, particularly songbirds. Her research concerned last year's eclipse; she had a hypothesis, though speculative, that an eclipse during a migratory month might trigger a long-haul instinct.

It didn't. The radar data she collected on the day of the eclipse showed that, as dusk fell, lots of birds across the country took flight, as normal. Biologists have several ideas why birds might chose night over day, as a 2009 study points out: Perhaps they're too busy foraging during the day. At night, the atmospheric conditions are more consistent, as cooler air is more stable. This is especially true for birds who are too small to take advantage of warm updrafts. Some species might orient themselves by starlight in the right directions. And predators would have a tougher time seeing birds in the dark. It could, of course, be a combination of these.

These night flocks are clumped looser, with birds flying in tandem yet up to 200 meters apart (imagine synchronized swimmers separated by two football fields). Researchers are still trying to piece together the mechanisms behind these night flights. Some biologists are using space telescopes to observe these nocturnal travelers. Others aim microphones at the night sky to listen to birds as they chatter and chirp. After all, nothing helps the miles pass like a good conversation.


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