Birds and Collisions

Collisions with Buildings, Towers, and Wind Turbines

Approximately 100 million to 1 billion birds die in North America as a result of collisions each year. (American Bird Conservancy, 2010) Primary sources of collision-related mortality for birds are building windows, communication towers, vehicles, transmission lines, and wind turbines. (US Fish & Wildlife Service, 2005) As the human population expands so does our need for communications towers, power transmission lines, and renewable energy sources. These threats are expected to increase for birds.

It appears that windows are the biggest source of avian mortality resulting from collisions. Birds collide with window glass because they often cannot detect the glass either because the glass is too transparent or reflective of the sky and clouds. Birds are often also attracted to light sources and plants inside buildings and collide with windows as they approach the attractants.

The American Bird Conservancy has provided the following estimates for sources of avian mortality arising from collisions in the United States:

Collisions with:

Year of estimate

Mortality estimate low

Mortality estimate high

Wind turbines








Power lines








Urban light







The death toll is significant and cannot be ignored by anyone concerned with conserving bird species and biodiversity in North America. For example, an estimated 5,000-10,000 Lapland Longspurs and other songbird species were killed by three communication towers in western Kansas in 1998. (See US Fish & Wildlife Service, 2010) In cities such as New York, Chicago and Toronto, volunteers have monitored bird collisions with tall buildings for years, documenting significant impacts to a large number of species. (See, e.g., Chicago Bird Monitoring Program, 2010) Between 1993 and 2005, volunteers in Toronto recovered more than 32,000 birds killed by collisions in Toronto. (Fatal Light Awareness Program, 2010) In 2008, New York City Audubon Society members monitored 338 birds that were killed by a single building in Manhattan. (New York Times, Feb. 3, 2009) Similar findings have have been recorded in other major metropolitan areas in the United States, and it is believed that data collected here reflect a global problem that has gone largely unstudied.

In San Francisco, several Peregrine Falcons have died in recent years as a result of collisions with buildings in the city’s Financial District. Golden Gate Audubon volunteers have reported several more resident and migratory bird species, including Green Heron and Red-breasted Sapsucker, that have died as a result of collisions with windows.

The severity of collision-related impacts to migratory bird species puts North American migratory bird populations at further risk. Of the 836 species of migratory birds in North America, at least one quarter are considered at risk according to the US Fish & Wildlife Service (and Golden Gate Audubon would put that number much higher).  (See US Fish & Wildlife Service, 2002) As of 2002, 78 migratory bird species were listed as endangered, 14 as threatened, and 144 were listed as species of conservation concern. (Id.) When combined with other impacts, such as habitat loss, unnaturally high predation from feral cats and other predators, collision risks contribute to the overall decline of many bird populations in North America.  (US Fish & Wildlife Service, 2005)

The killing of migratory birds is a violation of the Migratory Bird Treaty Act and constitutes a significant and ongoing threat to night-migrating bird species. (US Fish & Wildlife Service, 2000) The US Fish & Wildlife Service, several state wildlife agencies, and many private citizens and groups are working hard to reduce these unnecessary threats to birds.

What You Can Do

At Golden Gate Audubon, we’re working to reduce these risk to birds by helping develop Bird Safe Building Guidelines, promoting Lights Out for Birds, and working to reduce avian mortality in the Altamont Pass Wind Resource Area and other turbine installations. If you’d like to join Golden Gate Audubon’s efforts to reduce collision risks to birds, please contact us!

How to make windows in your home or office safer:

  • Use glass with special films, fritting, or whitewashing that makes it more visible to birds;
  • Hang reflective ribbons, chimes or other materials outside of windows that will catch the bird’s eye before collisions occurs;
  • Ensure that feeders and other attractants for birds are away from windows and in areas unlikely to result in a collisions if birds rapidly approach or flee from the feeder;
  • Avoid placing interior plants next to windows, where they may lure birds into a collision with the window;
  • Reduce your use of interior lighting when possible;
  • Draw the drapes or blinds on windows when possible, especially if you have noted a problem with bird collisions at the window before or at night when you are using interior lights.

(Sources: Fatal Light Awareness Program, 2010; American Bird Conservancy, 2010; Bird Conservation Network, 2005)

Additional Information:

Birds and Collisions:

How to Make Buildings Safer for Birds

News Stories

Reflective glass exteriors increase the chance of bird collisions / Photo by Allen Hirsch