Every year on September 11, two beams soar above Lower Manhattan in New York to pay tribute to those who were killed in the 9/11 terror attacks. Although the two beams are a way to remember those who were lost, they are putting one species at risk.
Birds can be spotted circling the lights as they are veered off course, putting them at risk of deadly exhaustion or injury, according to the New York Times.
The birds can also be heard calling to each other.
However, scientists say their calling only increases when they are confused.
The birds are often joined by insects and bats.
The heartbreaking anniversary of the attacks on New York’s World Trade Centre also coincides with the migration of birds across the city as autumn approaches.
According to one study, the lights endanger 160,000 birds a year that are migrating.
When the birds travel across the city, the beams of light send them on a detour which can put the birds at risk of starvation or injury.
Scientists have been working with ecological volunteers and the memorial’s sponsors to try to reduce harm to the birds.
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“The lights just sort of appear in the darkness and go on forever and when the sun rises the next morning it just disappears.
“It’s my job to turn the lights out, and I’d rather not have lights on at all, because the artificial light interferes with birds’ natural cues to navigate.”
Radar studies by Ms Elbin and other scientists show that the 20 minute breaks are enough to let the bird continue their migration.
The light beams attract birds up to 150 times their normal density levels.
One study showed that the lights affect the migrations of up to 1.1 million birds.
Ms Elbin said the lights leave the birds exhausted and disoriented which makes them vulnerable.
She continued: “Light lures them in, and glass finishes them off.”
Ms Elbin also said the lights cause the birds to use up too much of the fat they store especially for migration.
She added: “They only have enough to get where they need to go; the fatter you are the more energy it takes to fly, so it’s a fine balance.”
On Tuesday, the New York City Council is holding a meeting to require new or renovated buildings to use bird-friendly glass.