Millions of migrating birds will stream over Washington this week

More than 11.5 million birds are flying over Washington beginning Thursday night, a twice-yearly aerial torrent that goes unnoticed by most.

“I think it’s so mind blowing to even just imagine this river of birds flying overhead on their way up to the breeding grounds,” said Trina Bayard the director of bird conservation for Audubon Washington.

It’s a long and fraught journey from winter breeding grounds in the Gulf of Mexico and elsewhere to summer breeding grounds farther north.

And it’s a migration that’s made more difficult by light pollution.

In an effort to ease that passage, the Colorado State University Aeroeco Lab is urging Washingtonians to turn off nonessential outdoor lights Thursday and Friday nights. Roughly 2,600 birds will pass over Spokane Thursday night while 12,700 will fly over Seattle, according to the lab’s modeling. All told, more than 11 million birds will pass over Washington in the course of three days.

Those birds will be flying between 1,000 and 2,200 feet in the air, said Kyle Horton, a professor at Colorado State University who runs the Aeroeco Lab.

Roughly 70% of North America’s terrestrial birds are migratory and of those 80% migrate at night using the night sky to navigate. During the day they touch down near water and green space to rest.

However, light pollution can muddle their navigational skills leading to collisions with windows and walls. In Chicago, for instance 30,000 birds have collided with a single building over the course of two decades. It’s estimated that between 365 to 988 million birds die each year due to collisions, said Bayard.

But beyond the direct and obvious, a bird slamming into a window, lights can delay and confuse. The lights of a large city will draw birds into an environment that they normally would not go toward, delaying their journey and exposing them to urban danger.

“It all sort of adds up over time,” Horton said. “You’re increasing the odds of a lots of things. Colliding with a building or a glass. Or predation from a cat.”

One study, led by Horton, found that roughly 1.1 million migrating birds were attracted by the New York City September 11th Tribute in Light memorial over the course of seven years.

“But more importantly, when the lights were turned off, we saw (via radar) dramatic decreases in activity around the lights, taking no more than 20 minutes for the birds to dissipate,” according to Horton’s research.

But why are birds attracted to light? That remains a mystery, Horton said.

As for the aerial river of birds, that’s a relatively new discovery, although there were plenty of historical clues. For instance, 576 birds slammed into the Washington Monument in the space of just 1.5 hours one night 1937. And there are regular accounts of birds flocking to lighthouses or swarming fishing vessels far out on the Bering Sea at night.

But, the scope of this aerial migration remained unknown until World War II.

Radar – a means of detecting an object by bouncing high-frequency electromagnetic waves off it – was in its infancy and the British military, correctly predicting war, built several radar stations along Britian’s southern coast.

Almost immediately these radar installations started detecting mysterious slow-moving echoes that would dip, dive and often disappear completely. Called “angels” by operators they were an “operational nuisance.”

David Lack’s interest was piqued. A biologist (and pacifist) working for the British army he jumped at the chance to get out of the office and investigate. Lack and another military observer, George Varley, were the first to prove that these “angels” were actually birds. They did so using a powerful telescope on a clear day.

Thus the field of radar aeroecology (or radar ornithology) was born.

Now, researchers like Horton, use decades worth of radar data showing when and where birds flew. That data is linked with meterological data to predict when the most birds will be flying through the night at any given time. Birds heading north prefer a calm wind from the south, after all.

“We’re basically converting a weather type of map into a bird migration map,” Horton said. “We can then understand how many birds typically fly over the state of Washington. Then we can say, ‘OK, this night relative to all other night’s is quite intense.’ ”

All of which prompted the creation of the Lights Out alerts. The Audubon Society has its own system, although both pull from similar data and both emphasize giving the birds a break during peak migration season.

“There are some really easy and important steps people can take to reduce light pollution during this critical time for birds,” Bayard said.

Meanwhile, 39 cities have signed on to an Audubon-led Lights Out Campaign. No Washington cities have.

But what about seeing all those streaming birds? Models and science aside, it’s a bit hard to believe that millions of birds will travel overhead.

Horton recommends grabbing a pair of binoculars and training them at the nearly full moon to catch a silhouetted glimpse.

“It’s hard to visualize it,” he said. “They are up there. We can’t see them. We can barely hear them flying.”