NEW YORK (CBSNewYork) — The Tribute in Light memorial to the victims of the Sept. 11, 2001 attacks was briefly turned off at least three times Friday night, after birds became trapped in the beams of light.

The twin beams representing the fallen towers of the World Trade Center were first turned off shortly after 9 p.m., causing confusion among those viewing the memorial.

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The lights were turned back on about 20 minutes later, only to be turned off again around 10 p.m. They were turned on once more about 15 minutes later.

But the lights were turned off a third time around 10:50 p.m.

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David J. Ringer of the Audubon Society tweeted that the reason was that migratory songbirds had become trapped in the beams. He tweeted that weather patterns set up heavy migrations Friday night, and the beams had attracted the largest number of birds this year since at least 2010.

Ringer tweeted videos showing numerous birds flying around in the beams.

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The Audubon Society said in an article for reasons not clear scientifically, artificial light attracts an assortment of birds, from fledgling seabirds to migratory songbirds – in the same way as it does for moths.

Once birds get stuck in the light, they can spend hours flying in circles or crash into windows, the Audubon Society said.

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The 9/11 tribute is particularly difficult for birds, as its dozens of 7,000-watt bulbs reach four miles into the sky, the society said. Thus, Audubon Society representatives are always on hand to monitor the situation, the society said.