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ZEISS DTI thermal imaging cameras. For more discoveries at night, and during the day.

Night migration - New York City (1 Viewer)

Katy Penland

Well-known member
Thought members would find the below interesting:



NEW YORK TIMES
May 21, 2006

Listening to the Faint Flutter of Birds Passing in the Night

By TINA KELLEY

Who knew there was a noise for this? And not just one noise, but a billionfold chirping, all night long, all spring, all fall, barely audible but as elemental as the grinding of the Earth on its axis.

The birds are heading north for the summer.

Jeff Wells, an avian ecologist, shared the tiny calls, slightly amplified, at a Nocturnal Bird Migration Concert Friday night at the Prospect Park Audubon Center.

A simple high-powered microphone was set up on the center's roof, connected to Dr. Wells' computer, which displayed pictures of birds that migrate through the city at this time of year. He also showed spectrograms, or pictures of their calls as ascending or descending black zigzag ribbons, the audible thumbprint of each species.

"I want to let you in on this great secret, a great mystery only a tiny, tiny number of people in the world ever know about," he told a group of about 25 people, his voice hypnotic in its wonderment.

"They're all up there in the air, migrating while we sleep, on high highways of wind," said Dr. Wells, the senior scientist at the Boreal Songbird Initiative, a conservation group that tries to protect the endangered boreal, or northern, forest that stretches from Alaska to Newfoundland and is the summer home of three to five billion birds.

Birds migrate at night to avoid predators, he said, and because the atmosphere tends to be calmer. They also may be able to use celestial cues better in the dark.

There are various ways to view birds at night. Some avid birdwatchers train their scopes on the full moon and wait until the quick silhouettes of migrants pass, "but that's kind of like watching a baseball game through a paper towel tube focusing on first base," Dr. Wells said.

Clouds of migrating birds are also picked up on weather radar screens, he explained, guiding his computer to the Doppler radar station on weather.noaa.gov/radar/national.html. The blocky dots are rain showers and clouds, he said, but smaller dots are likely birds.

Then it is possible simply to listen. Birds call all the time while flying, he said, and in the spring some break into song overhead.

A high-powered microphone can be set up at home, even in the city.

"Cities are often best, because there are a lot of lights, and they're near the coast," Dr. Wells said. Birds can get confused by bright lights, which makes them call to each other more frequently.

At the Web site www.oldbird.org, instructions show how to build a microphone on a plastic-wrapped dinner plate, kept inside a flower pot, for about $10 (look toward the bottom of the listing on microphone design). It also offers free software that sifts through the various calls overnight, producing spectrograms and keys to identifying what bird produced them.

"I warn any of you to be careful: You won't sleep at night," Dr. Wells said. "And in the morning, you'll have to run right to your computer to find out what went over your house all night."

After describing the boreal forest and how 2.5 million acres in North America are lost to development or logging each year, mostly to provide paper to the United States, he projected a picture of a starlit sky on the screen.

"Maybe you're on a nice remote beach, or on a hill, or up on top of your brownstone," he said, turning up the sound from the microphone outside. "You're just kind of out listening to the sky."

The sounds drifted in: a siren moving closer, an airplane soaring down to La Guardia. Was that a dog barking or a night heron?

Dr. Wells, who lives in Maine, asked if there would be dogs in the park this late. Yes, someone answered. But there were also night herons.

At 9:45, over the course of 10 seconds, four bird calls came in. Swainson's thrush, Dr. Wells said with some certainty. More birds usually pass over after 10.

"If you know to put your ears up and listen, you'll hear birds, and life is changed forever," he said. "You can't step out without saying, 'My God, there's a current of birds going overhead.' "
 
I acknowledge that I'm late to the party on this. As an amateur astronomer, I have at times heard an occasional bird call from overhead during migration season, but I've never heard them in large numbers. Maybe I'm just not trying hard enough. I've also occasionally seen birds fly in front of the Moon or Sun (I have a Coronado solar scope). When I first noticed these, I imagined that the birds were at great distances and heights, but I finally did some calculations with some generic but reasonable assumptions about the angular size of the bird and species, and it appears that usually they are no further than 2 to 4 miles away and no higher than 1,000 to 2,000 feet. One of my books gives a migration altitude of as high as 14,000 feet for some warblers, but other reading suggests that this would be the exception.
 
The recently published book, "Songbird Journeys" by Cornell Lab Ornithologist, Miyoko Chu is really worth a read if you are into North American songbird migration. Birdsong by Don Stap is also brings migration and songs to life.
 
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