There is growing awareness of the danger that tall buildings pose to migratory birds; for example it’s estimated that upwards of 100 million die in collisions with North American buildings every year. Chicago, for instance, lies squarely on the Mississippi Fly way, used by enormous numbers of birds in spring and autumn. The risks are greatest to night migrants, which are attracted to or disoriented by buildings lit up like beacons.

So most Chicago skyscrapers now dim their lighting or switch it off altogether from 11pm to sunrise during the migration season – a study of one city building found this reduced bird deaths by 83 per cent. A group called Chicago Bird Collision Monitors promotes bird-safe lighting and building design. “We want the birds that are making such amazing migratory journeys to have safer passages through our urban areas,” says its director Annette Prince.