According to bird migration expert Christian Booth, of the University of Groningen, last Monday’s storm was likely the reason so many birds are now at the bottom of the towers. “If migratory birds have a headwind, they fly at a lower altitude than when they have a tailwind. Because of the storm, they are out of the buildings height.”

Bright light also has an attractive effect on animals. “Migratory birds sail by the light of the moon and stars, but the light in the buildings makes them disoriented,” Booth says.

Turn off the lights

Therefore, Bird Conservancy is calling on the World Trade Center to turn off the towers’ lights during the birds’ migration, and to adapt the buildings in a way that birds can see better.

A spokesperson for the skyscrapers project developer says migratory birds have been taken into account in the design. “For example, the first sixty meters of glass are not reflective.” Office building tenants are also required to turn off their lights during the migration of birds.

Booth says this type of bird death is less common in the Netherlands. “This is because the difference between light and dark is smaller in the Netherlands.”

Some birds survived the collision with the skyscraper. 77 animals were collected and cared for by Bird Conservancy.