 Mourning Warbler |
The piercing beams of New York City’s 9-11 Memorial trace the outlines of the fallen Twin Towers and help us remember an American tragedy. Now, through research by Cornell Lab of Ornithology scientists and volunteers at New York City Audubon, those lights pose less of a threat to migratory birds. Songbirds such as warblers, tanagers, vireos and thrushes migrate at night and navigate by the stars, but they can become confused by artificial lights, sometimes leading to fatal collisions with buildings.
Early September is peak migration season for many neotropical species and up to 420 million birds have been recorded passing south each night in the United States during this time. Cornell Lab ornithologists estimate that up to one-half of the continent-wide migration occurs on just 10 nights, increasing the stakes for nocturnal migrants that could be distracted by the 9-11 light beams that can be seen 40 miles away.
Radar indicates the 9-11 Memorial lights sometimes attract nocturnal migrants at up to 150 times their normal densities. To prevent the lights from becoming a hazard, Audubon volunteers count birds in the light beams. If the densities exceed more than 1,000 birds, or if a bird fatality is recorded, the lights are turned off, allowing the birds to disburse.
On September 11, 2010, the lights were shut off for the first time; during 2015, the lights were turned off a record nine times. Cornell ornithologists can see the benefits of turning the lights off by watching radar images: Bright orange and red pixels change to cool blues as the concentrated birds return to normal migration patterns. The system is working! Remarkably, only two warblers have been found dead since the monitoring program began.
Article by Peter Stangel