9/11 lights misleading migratory birds

'They end up burning energy without making any progress, risk colliding with buildings' says Benjamin Van Doren

The behaviour of migratory birds was found to be affected by the two blue beams of light projected in the sky to commemorate the September 11 attacks on the World Trade Centre in 2001.

Scientists from the University of Oxford, Cornell Lab of Ornithology and New York City Audubon monitored migrant bird behaviour over seven years as the searchlights create two vertical columns of light to mirror the twin towers annually. The 'Tribute in Light' art installation is formed by 44 zenon bulbs of 7,000-watt intensity and is lit up every year on the anniversary of the tragedy.



Migratory birds are often attracted to and influenced by light, which significantly affects their behaviour in the presence of artificial lights at night. According to the University of Oxford, billions of birds migrate during the spring and autumn months.

A study published in the Proceedings of the National Academy of Sciences offers solid evidence of drastic changes in the behaviour of migratory birds due to artificial light during the night.

“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,” said Benjamin Van Doren, lead author from the Oxford’s department of zoology.

Co-author Kyle Horton of Cornell Lab said that the art installation provided a rare chance to examine the influence powerful, urban, ground-based lights have on migratory birds. The lights are turned off by the National September 11 Memorial & Museum for 20 minutes when more than a thousand birds start encircling the beams or flying perilously low and risk crashing into one of the buildings.



The 20-minute switch-off provides a rare opportunity for scientists to quantify the changes in bird behaviour in different ways during the alternating episodes of light and dark. When the tribute was lit up, the researchers found that densities of birds over lower Manhattan could escalate 60 to 150 times the usual average in the area.

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

This story originally appeared on Hindustan Times.