© Kim Carpenter, Wikimedia Commons
Hundreds of bird deaths were averted in a scene strangely reminiscent of 9-11 shortly after midnight on Sept. 12, when twin columns of bright lights that had attracted thousands of migrating birds from the sky above New York City were turned off several times to let the birds pass by unharmed.

The lights are the main attraction of New York City's annual "Tribute in Light" memorial to those lost in the 2001 attack on the World Trade Center. However, the light show also is a seasonal hazard to migratory birds in a city with an estimated 90,000 bird deaths annually due to collisions with buildings.

This video by Andrew Farnsworth shows birds spiraling downward during the 'Tribute in Light' 9-11 memorial. Bird deaths were averted when organizers turned off the lights.

"What we saw last night was the birds coming down," said Susan Elbin, director of conservation and science with New York City Audubon. " You could hear them calling, and as the birds came lower and lower, filling up the light beams, their calls got louder and louder and we no longer needed binoculars to identify them."

Elbin and a team of Audubon volunteers were positioned at the base of the lights on the roof of a parking garage with a team of lighting technicians with the Municipal Art Society of New York, organizer of the annual tribute. The local New York City chapter of the National Audubon Society has about 3,000 members and many of them, including the Tribute in Light volunteers, have vivid personal memories of 9-11.

© John Harrison
he Rose-breasted Grosbeakswas one of the species of migrating songbirds that averted death thanks to New York City Audubon and the organizers of the Tribute in Light memorial in New York City on Sept. 11, 2013.
"I had a colleague who passed away in 9-11," Elbin said. "It was really moving to be a part of the Tribute in Light memorial, which turned out to be a wonderful conservation story this year."

The bird species disoriented in the twin lights included American Redstart, Canada Warbler, Black-throated Blue Warbler, Swainson's Thrush, Wood Thrush and Rose-breasted Grosbeak. However, Elbin told a Wired reporter that a Peregrine Falcon also was spotted.

When Elbin saw more and more birds spiraling downward toward the light, seemingly "spilling down from the sky," she immediately contacted the Tribute in Light production manager Michael Ahern and his team.

Bird deaths averted

New York's birding community said Ahern was masterful, balancing a dignified celebration with real-time conservation. He didn't want the lights to cause bird deaths.

Elbin negotiated with Ahern's team to shut off the lights four times, 30 minutes each time, between midnight and 4 a.m., Sept. 12. When the lights were turned off, the circling, disoriented birds quickly moved on, apparently able to regain their bearings and fly south at higher altitude.

Each time the lights were turned off, the birds' chirping calls, possibly made out of alarm, quickly subsided, Elbin said.

The local chapter of the National Audubon Society assumed days in advance that Sept. 11 and 12 would be low-traffic nights for migrating birds. BirdCast, a migration-forecasting system being developed by the Cornell Lab or Ornithology, Oregon State University and the University of Massachusetts, Amherst, had predicted few birds would be migrating through New York during the memorial event.

But those predictions were off the mark.

"Migratory birds have some incredible abilities to understand optimal weather conditions for migration," said Andrew Farnsworth, an ornithologist with the Cornell Lab of Ornithology and the lead scientists for BirdCast.

The birds made full use those abilities on Sept. 11-12. Farnsworth was on the roof of the New York City parking garage with Elbin and her team, when the sudden appearance of birds in the lights surprised him.

At first, hundreds, and then thousands, of migrants appeared in the light beams. "BirdCast did not account for a very local weather phenomenon called gust fronts associated with thunderstorms," Farnsworth said in his blog.

He said the gust fronts inspired birds in Connecticut to take flight in less marginal migration conditions than he expected. The experience will help BirdCast scientists factor in such local weather events to make their predictions more accurate on smaller scales.

This video of National Weather Service showing storm systems moving north through New England also reveals airborne flocks of birds migrating from Connecticut through the New York City area to central New jersey, as indicated by the doppler-radar-generated blue patches in those areas.

The BirdCast system relies on radar images and weather data from the National Weather Service as well as millions of sightings of volunteer birders that have been entered into a huge database called eBird. An artificial intelligence algorithm uses all the information to generate predictions of migrations on a broad scale.

"Our interpretation of all the data available is steadily improving, and some people who have seen our first analyses were blown away to see how migration direction changes over the Atlantic or Appalachians," Farnsworth said. "I also think there will be some practical applications, such as being able to advise municipalities to turn off their lights and wind farms to turn off their blades. We're just starting to realize the cool science that will come out of this."