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9/11 lights play havoc with migratory bird behaviour

A new study offers compelling evidence that the two blue beams of light mirroring the twin towers of the World Trade Center cause radical changes in the behaviour of migrating birds.  

world Updated: Oct 03, 2017 07:39 IST
Prasun Sonwalkar
Prasun Sonwalkar
Hindustan Times, London
September 11,9/11,Terror Attack
The beams of light symbolising the two World Trade Center towers the night before the 15th anniversary of the September 11, 2001 terrorist attacks in the United States on September 10, 2016 in New York.(AP File Photo)

The two powerful blue beams of light that commemorate the September 11 terror attacks in New Yorkhave been radically changing the behaviour of migratory birds, according to new research by British and American experts.

Over seven years, scientists from the University of Oxford, Cornell Lab of Ornithology and New York City Audubon studied migrant bird behaviour in the unique setting of the “Tribute in Light” art installation that commemorates the September 11, 2001 terror attacks.

In honour of the anniversary of the tragedy, two blue beams of light - formed by 44 xenon bulbs of 7,000-watt intensity - shine into the night sky, mirroring the twin towers of the World Trade Center.

Migratory birds are both attracted to and influenced by light. As a result, their behaviour alters drastically in the presence of artificial light at night. Every year, billions of birds undertake migratory journeys during the spring and autumn months, the University of Oxford said.

However, the new study published in the Proceedings of the National Academy of Sciences offers compelling evidence that artificial light at night causes radical changes in the behaviour of migrating birds.

Benjamin Van Doren, lead author from the Oxford’s department of zoology, said: “We found that migrating birds gather in large numbers over New York City because they’re attracted to the lights. They slow down, start circling, and call more frequently.

“They end up burning energy without making any progress and risk colliding with nearby buildings or being caught by predators.”

Co-author Kyle Horton of Cornell Lab said it was a rare opportunity to witness the impact of powerful, urban, ground-based lights on nocturnally migrating birds.

The National September 11 Memorial & Museum turns off the lights for 20 minutes when more than 1,000 birds are seen circling in the beams or flying dangerously low, to the point that they could crash into buildings.

The 20-minute switch-off provided a unique opportunity for the scientists to quantify changes in bird behaviour in several ways during the alternating periods of light and dark.

When the tribute was illuminated, the study’s authors found that densities of birds over lower Manhattan could reach 60 to 150 times the number than what would typically be found in the area at that time.

The concentrating effects of the intense light on the birds reached as high as 4 km, even on clear nights, in contrast with many previous studies that highlight the dangers of artificial light and nights with poor visibility. When the light beams were turned off, the birds dispersed within minutes to continue their migrations.

First Published: Oct 03, 2017 07:18 IST