Cross lighting results in mass avicide

By Vanessa Moss

Executive Staff

Early in the morning of September 27, a Sewanee leaseholder was taking a daybreak stroll to the Memorial Cross when they stumbled upon what must have seemed like an abandoned warzone. Over 130 bird carcasses were strewn around the Cross, each with a significant mechanical injury: broken wings, crushed ribs, and hurt necks left members of 22 different migratory species dead on the ground.

As soon as Domain Manager Nate Wilson got into the Office of Environmental Stewardship and Sustainability at 8:00 a.m., he received a call from that distressed leaseholder informing him of the numerous dead birds.

After inspecting the site alongside Domain Ranger Sandy Gilliam, Wilson returned to his office to make several phone calls, one of which was to Biology Professor David Haskell. Haskell explained that he had “seen smaller (half dozen at a time) bird kills at the cross, all after foggy nights.”

These birds were trapped by an inconspicuous killer: the 2,000-watt spotlights shining all night on the Cross.

Strong northwest winds blew over the mountain the evening of September 26. The night was brisk; a cold front had just arrived, giving campus a false hope for fall weather. A thick, low fog settled throughout Sewanee.

The rare confluence of these conditions led to the birds’ demise. The northwest winds during the peak of migratory season created the perfect condition for nocturnal migratory birds to travel south, but the cold front caused the birds to fly lower than normal, avoiding the freezing temperatures higher in the sky. The lowered flight ceiling, in conjunction with the reflective fog, made the birds much more susceptible to being caught in the arched roof of the spotlights’ glare.

Researchers understand that night migratory birds’ directional senses are thrown askew when faced with intense artificial light, and have recently discovered that bright red and white lights disrupt nocturnal migrators’ natural magnetic compass, causing them to fly in circles around the source of the light until exhaustion or, in the case of the Memorial Cross, an edifice in and around the light source causes their death.

Before noon on September 27, Wilson and Gilliam held a meeting with Trades Manager of PPS Greg Rollins and Superintendent of Landscape Planning and Operations for PPS William Shealy to discuss solutions to keep a migratory bird kill of this size from happening again on the domain.

They quickly switched the 2,000-watt bulbs in the spotlights to 200-watt LED bulbs, that emitted an 800-watt equivalent light intensity, cutting the spotlight’s electrical usage down tenfold, and reducing the light intensity by almost two thirds. Although the fall migratory season has come to a close, PPS and the office of Environmental Stewardship and Sustainability will monitor the Cross closely for the spring migratory season.

If the reduction of light intensity is not enough to keep from causing bird kills,steps will be taken to turn off the Cross’s spotlights for 20-30 minutes at specific times during the night, allowing the birds to reorient themselves and take off on their migratory path again. The “Memorial in Light” 9/11 memorial in New York uses this tactic,advised by the Cornell Lab of Ornithology.

The offices of Environmental Stewardship and Sustainability and Physical Plant Services not only responded to this issue rapidly and with personal resolve, but they recorded the event in an Incident Report for Cornell University, and the specimens themselves have been sent to Southeastern Cooperative Wildlife Disease Study for further study. Haskell commended the offices, “I applaud the rapid response of my colleagues. They are putting in place an excellent plan to avoid this kind of event in the future.”