WILLIAMSBURG, Va. (AP) — Every spring and fall in the city of Chicago comes a strange and terrible sort of carnage: sidewalks littered with the carcasses of birds.
Common birds, rare birds. Small birds, large birds. All victims of their anatomy, their migratory instinct and the skyscrapers built in their ancestral flyway along the shore of Lake Michigan.
So many dead birds, in fact, that they make up a major portion of the specimens in Chicago's prestigious Field Museum of Natural History.
"They've gone out early in the morning and collected even rare species that are migrating through," said John Swaddle, a biology professor at the College of William and Mary in Williamsburg who did post-doctoral work at the University of Chicago. "When one of the curators told me that a fair part of their collection was determined by bird strikes, that was eye-opening to me."
But it's not just the Windy City — the same happens in other major metropolises with buildings that tower like brick-and-mortar islands in a sea of sky.
The result? Roughly a billion birds in North America that crash and die every year.
Swaddle hopes to fix that.
He's developing an alarm system of sorts that would warn off migrating birds as they approach a tall building, cell tower or wind turbine.
He calls his emerging technology an "acoustic lighthouse." It's already undergone a proof-of-concept in the college aviary, and now Swaddle is pursuing grant or industry funding that will enable him to take it for a test-drive in an outdoor setting, hopefully in the next year or two.
The reason migrating birds crash into tall, man-made structures is actually pretty straightforward, said Swaddle: "They're not really looking where they're going."
And it's not their fault — they're just built that way.
"When we're walking around, we see directly in front of us because our eyes are placed right in the front of our skulls and our heads are up," Swaddle explained. "But a bird, when it flies, its head is slightly down and its eyes are positioned on the sides of its skull more than on the front of its skull. So it doesn't really get that great a view of what's directly in front of it.
"When a bird is in level flight, cruising around, especially during migration, the body is fairly flat, horizontal. That means that, the way the eyes are positioned on a bird, the field of view is largely pointed down and to the side, and not directly in front."
This adaptation makes great evolutionary sense for a natural environment, he said, because a bird in flight is navigating by cues on the ground — a lake over here, trees over there. They're also keeping an eye out for predators and foraging for food.
"So what we wanted to do was see if we could grab the attention of the birds to look more directly in front of them," said Swaddle. "To reduce the risk of, say, them flying into a window or a skyscraper."
The acoustic lighthouse essentially consists of a flat-panel speaker, an amplifier and a system to produce a particular sound — in this case, a sort of white noise that resembles radio static.
"Something that's very unusual for a bird to hear, and I think that's the crucial thing," Swaddle said. "It's got to be both novel and conspicuous. Something that's not easily confused with, say, traffic noise or air-conditioning noise. It's got to be something that grabs their attention."
Swaddle tested the concept using the aviary's zebra finches. First, he trained the finches to fly the length of a corridor unimpeded. Then he introduced a mist net — a very fine-mesh net used to safely capture birds in the field.
As expected, zebra finches flying in the corridor flew into the netting. Then Swaddle introduced a very conspicuous sound field right in front of the mist net.
The result, he said, was that finches entering the sound field abruptly altered their flight position — angling the body from horizontal to more vertical, tipping the tail down, bringing the head up to better see what's in front.
"Slamming on the brakes," said Swaddle. Some avoided the mist net entirely.
When finally operational, an acoustic lighthouse would be mounted on the exterior of buildings several stories up where the static wouldn't annoy pedestrians below or people inside. Perhaps a bird radar would trigger the signal as needed, aimed at an approaching flock while it was still about 50 meters off, giving plenty of warning.
The idea is for building designers, city planners and others to coordinate to ensure the technology is strategically placed for best effect, especially among multiple buildings in the same area.
"You wouldn't want to get birds trapped in a little area or pockets of quiet and get them all confused," said Swaddle.
The technology might even be useful at college campuses, he said, which are often built next to wooded areas and tend to have libraries, museums or other signature buildings with large windows to let in lots of light.
In fact, Old Dominion University in Norfolk recently published a study on how such campus collisions are impacting bird species and populations.
According to ODU, Eric Walters, an assistant professor in biological sciences, and Natasha Hagemeyer, a doctoral student in ecological sciences, were part of a three-year nationwide survey of window strikes organized through the Ecological Research as Education Network.
An international team of more than 60 researchers monitored nearly 300 buildings at 40 North American campuses, including ODU, which sits in the middle of the Atlantic Flyway.
Researchers found a total of 324 bird carcasses from window strikes, averaging 8.1 per site. The study was just published in the science journal "Biological Conservation."
According to the website News@ODU, Hagemeyer said birds just aren't used to reflective surfaces.
"There aren't any large, transparent objects in the wild, and mirrored windows can reflect habitats," said Hagemeyer.
Recognizing this, Swaddle and the student bird club at William and Mary set out last year to make some of their campus buildings less deadly.
Calandra Waters Lake, director of sustainability at the college, said they've funded two projects to reduce window strikes.
"I would say that the William and Mary bird strike challenges on campus are not unique," said Lake. "But we take sustainability seriously, and we wanted to do what we could to help reduce their occurrences — especially on buildings that had more window strikes than others."
Using funds from the student "green fee" that's dedicated to environmental and sustainability efforts, they purchased special window film for Swem Library and the Muscarelle Museum of Art.
"It reduces the glare of the windows," Lake said. "And some of them have patterns that are very hard to see if you're just walking past the building, but it breaks up the reflection and allows birds to really notice the window more than before."
She said they've seen a reduction in bird strikes since the films were installed.
But a major area with real potential for an acoustic lighthouse, said Swaddle, is the wind turbine industry.
According to a study published in Biological Conservation in 2013, as many as 328,000 birds die each year in the U.S. from collisions with wind turbines.
That risk presents a real barrier in some parts of the country to developing wind energy, said Swaddle, including Dominion Energy's stated plan to develop offshore Virginia.
"It was a significant part of what Dominion had to go through to get their offshore siting license," said Swaddle, "because our coastline is a pretty significant migratory flyway for lots of species of birds."
Could his acoustic lighthouse eliminate or reduce that strike risk?
"It's too early to say whether it'll work," said Swaddle. "The data that we have is certainly promising and indicates that. But we need to take those next steps of taking the work outside the controlled conditions we have and testing it in more realistic conditions.
"But, yes, that's one of the end uses we potentially see. And hopefully that's one of the end uses that other people see, as well, and might want to get involved in the work that we're doing to sort of take it to that point sooner rather than later."