Migratory birds and city lights
Every year, thousands of birds are injured or killed on migratory pathways when they became confused by city lights. Many more birds are killed by collisions with buildings than by oil spills. In fact, an estimated one hundred million to one billion birds die each year due to collisions with human-built structures across North America alone.
Why are lights dangerous to birds?
In spring, some bird species fly from the United States, Mexico, the Caribbean or South America to reach summer breeding grounds in Canada. In the fall, they make the return journey. Many of these species migrate at night.
Stars help birds find their way, and artificial lights from tall buildings, broadcast towers or any other structure that obscures starlight can disorient them. Fog, rain and low clouds reflect light, making it even harder for the birds to find their way.
What happens to disoriented birds?
Birds that become disoriented by artificial light will either collide with a structure or fly around it until they become exhausted and drop. Birds can also be “trapped” by beams of light. Once in a beam, birds are reluctant to fly out of it into the dark. They flap around in the lit area until they fall from exhaustion.
After a collision or fall, birds can die from injuries like head trauma, broken beaks and feather damage. Many birds are only stunned by a collision and recover from the shock after a couple of hours. But if they find themselves surrounded by bright city lights, they won’t have a very good chance at survival. If they haven’t found their way out by morning, many birds panic when the city comes to life, which can cause them to hit more windows. If they manage to avoid collisions, they are still at risk from predators, like cats and gulls, or even starvation.
What can be done?
Migrating birds are threatened by a variety of human activities, so it is important to minimize impact wherever possible. The public, office building management and staff can be taught to understand the risk to birds and help by turning off or dimming unnecessary lights.
HSI Canada is working with the city of Toronto and other organizations to raise awareness of the hazard that illuminated office towers pose to birds during the migration season. The groups want to establish bird-friendly policies and practices that will help keep migratory birds alive on their way through Toronto.