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Last edited 16 Mar 2021
Lights Out: Protecting migratory birds from illuminated skyscrapers
|This peregrine falcon is captured in flight in front of Philadelphia's City Hall.|
Architects often use glass to connect the inside and outside, but unfortunately it can literally kill the nature it attempts to put on display. In the UK, the British Trust for Ornithology estimates up to 30 million birds die every year from window strikes. In the US, up to a billion birds die each year when they collide with buildings, because they fly towards their bright, artificial lights turned on at night.
 Night time illumination, skyscrapers and window strikes
Built up environments increasingly occupy or interrupt migratory routes, and artificial lighting inside these buildings can attract or confuse birds that migrate at night. Bird strikes typically increase during migratory seasons, as non-native species travel through towns and cities in unfamiliar landscapes.
These birds use natural cues - such as the earth’s magnetic field and the position of the stars - which is why artificial lighting on large panes of glass can be problematic for them. During cloudy weather, when natural cues may be obscured, birds may be even more attracted to artificial lighting.
Window strikes from birds can occur in skyscrapers when the large panes of glass act like mirrors. While strikes can happen at all levels of the building facade, they tend to happen most often in the levels comparable to those of the tree canopy.
For birds - whose eyes are positioned in such a way that makes it difficult for them to process visual information that is directly in front of them - this can create a misleading optical illusion of a clear passageway. Indoor plants and outdoor trees close to buildings can add to the confusion. Birds can die due to exhaustion brought about by disorientation.
In 1999, Audubon introduced a Lights Out programme following monitoring of migratory bird strike data during the spring and fall. Those were times of year when artificial lights on at night (ALAN) and reflective and transparent glass had the most damaging effect on birds that migrate at night.
Lights Out was first introduced in Chicago and has since been adopted by cities throughout the US. In 2021, Philadelphia joined New York, Boston, Atlanta, Dallas, Cincinnati, Detroit, San Francisco and many other cities across the country.
The national initiative is a voluntary programme that involves turning off or blocking as many external and internal building lights as possible at night during migration seasons when birds are passing through the city by the millions. As part of the programme, property managers and their tenants are asked to turn off unnecessary lights between midnight and 6 a.m., especially in a building’s upper levels, lobbies and atriums, and to turn off or dim external lighting.
 Related articles on Designing Buildings Wiki
- Birds and building collisions.
- Bird deterrent programmes.
- Parleys Canyon Wildlife Bridge.
- Protected species.
- Spontaneous City at Cow Tower.
- Window screens.
- Wired glass.
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