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9/11 memorial Lights are Hazardous to Birds

A seven-year study has revealed that the 9/11 memorial light display in New York is disrupting migrating birds. The stunning lights, which reach up to the sky above Manhattan where the Twin Towers once stood, are an amazing sight but could threaten wildlife.

Dr Susan Elbin, New York City Audubon's Director of Conservation and Science, co-authored a report with researchers from Oxford University and the Cornell Lab of Ornithology following the study. This was recently published in the Proceedings of the National Academy of Sciences.

Birds Drawn to Manhattan Lights

During the study, the researchers observed that thousands of birds tended to be drawn to the annual memorial light display. This caused the birds to waste precious energy as they circled the lights. They were also at risk of colliding with buildings or being captured by predators.

Nocturnal Migration

Birds often travel at night when migrating. They are increasingly forced to travel through light polluted skies. Under a protocol established in 2002 to prevent harm to migrating birds, the tribute lights of the World Trade Centre are switched off for 20 minutes whenever more than 1,000 birds are seen to be circling or flying dangerously low with frequent calling. These interludes of darkness enabled the scientists to quantify changes in bird behaviour. More than twenty volunteers were enlisted to count the birds.

Massive Increases in Birds

In 2015, the number of birds counted within 500 metres of the lights rose from 500 to 15,700 within 30 minutes of the lights being switched on. When the lights were turned off again, the birds dispersed in just a few minutes. Data provided by the National Weather Service radar helped document the density and movements of the birds. Acoustic monitors recorded their vocalizations.

A Million and More Birds

The study’s report estimates that the lights have influenced more than a million birds including warblers, thrushes and sparrows in the seven years of monitoring. However, it wasn’t possible for the researchers to gain an accurate assessment of the number of deaths which occurred as a result this was because some birds would have fallen onto scaffolding, would have been taken by scavengers or may have been disposed of by building and maintenance workers. Their bodies, therefore, could not be identified and counted.


The authors of the report have recommended that lights around homes, sports stadiums, offshore oil rigs and construction sites should be turned off as much as possible during the migration season. The period between midnight and first light is particularly crucial.

It would appear that there are few forms of human activity which do not impact wildlife. The memorial lights are a striking and well-meaning tribute to the victims of a terrorist attack. But in reminding us of an incident in which planes flew into buildings, they are causing more deaths by causing birds to fly into buildings.


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