Chicago tops the list, with its many skyscrapers of glass and its location, the city is the largest dödsfällan, in particular for migratory birds. Over five million birds of 250 different species passes through Chicago every spring and autumn, writes The Guardian.

go in the spring from Central and south America, across the Great lakes in north America up to Canada, and back south in the autumn.

most of The migratory birds make their movements at night when it is cool and windless. At the same time, it is since long known that birds are drawn to light, so when they are flying over a lit up city at night, it is natural that they are attracted by the light, unaware of the danger.

– They end up in a place that is unfamiliar, such as on a sidewalk somewhere. When daylight comes, they fly to a tree in search of food, or what they perceive as a tree but which in reality is a reflection in a glass building … Then they fly straight into the glass and die, ” says Susan Elbin, director of the New York City Audubon, a leading organization for bird watching.

in byggnadskollisioner is not possible to determine exactly the. But New York City Audubons field studies on the city’s streets estimates that between 90.000 and 200.000 birds are killed in byggnadskollisioner in New York city each year.

At the national level in the US, the figure is 100 million up to a billion birds die this way annually, according to estimates by the Smithsonians migrationsfågelscentrum writes The Guardian.

Recently published a study which developed which cities in the united states that is most dangerous for the birds and there came the Chicago, Houston and Dallas in the top, followed by New York, Los Angeles, St. Louis and Atlanta.

in Order to reduce the collision is sufficient for scientists to urban planners faced a more fågelvänlig environment. It can for example be to reduce street lighting on and off lights in skyscrapers at night during the week when the migratory birds are most active. It would make a big difference, according to the researchers.

building houses that are more ”fågelvänliga”, for example with patterned glass and dimmer-controlled lighting on the facade.

San Francisco and Toronto have already adopted fågelvänliga guidelines, New York and Chicago are in the pipeline. There is also a proposal in the u.s. congress to take a more fågelvänlig the urban environment.

” We are a part of the ecosystem just like the birds. It is good for birds is good for people, ” says Susan Elbin.