Wired Science | 14 Sept 2010
On the evening of the ninth anniversary of 9/11, the twin columns of light projected as a memorial over the World Trade Center site became a source of mystery.
Illuminated in the beams were thousands of small white objects, sparkling and spiraling, unlike anything seen on other nights. Some viewers wondered if they were scraps of paper or plastic caught in updrafts from the spotlights’ heat. From beneath, it was at times like gazing into a snowstorm. It was hard not to think of souls.
Those unidentified objects have now been identified as birds, pulled from their migratory path and bedazzled by the light in a perfect, poignant storm of avian disorientation.
“It’s only happened once before. It’s a confluence of circumstances that come together to cause this,” said John Rowden, citizen science director at the Audubon Society’s New York chapter. “Some of it has to do with meteorological conditions, and some with the phase of the moon.”
New York City sits in the middle of a major migration corridor, used for millennia by birds flying south for the winter. During autumn nights, thousands of birds pass directly above the megalopolis, a passage generally unnoticed by its human inhabitants.
During the previous week, weather was bad for migration. Tropical storm systems moved north up the U.S. East Coast, pushing against birds headed south. To conserve energy, migratory birds prefer tailwinds, and are willing to wait for good weather.
“Birds were coming down from the north and piling up, waiting to push southwards,” said Rowden.
To navigate, birds rely on a variety of internal compass mechanisms, which are calibrated to Earth’s geomagnetic fields by sunlight, starlight and moonlight. On Sept. 11, the new moon was just two nights old, a thumbnail sliver. In such conditions, birds rely on starlight, but parts of the lower Manhattan sky were overcast.
The buildings resembled stars. Outshining them all was the Tribute in Light above Ground Zero.
