Collisions with buildings add up to second-highest cause of death for birds in the U.S.

(January 22, 2014, The Condor: Ornithological Applications)—Maybe you’ve heard a jarring thump against your house, or perhaps you’ve seen the telltale white impression of a bird on a window. Researchers estimate in a study published in the scientific journal The Condor: Ornithological Applications that about 600 million (and possibly up to 1 billion) birds die each year from collisions with buildings, and especially windows, in the U.S.

Bird–building collisions are the second-highest cause of death in birds in the U.S. caused by humans—only feral and free-ranging pet cats kill more birds than building collisions, says lead author and Oklahoma State University Assistant Professor Scott R. Loss. Researchers also learned that some types of birds are more likely to collide with buildings. The report is the first of its kind to use data from multiple studies to estimate the number of birds killed each year by collisions with U.S. buildings.

Researchers found that the sheer number of residences (detached houses 1 to 3 stories tall) in the U.S. means that these domiciles contribute to about 253 million bird deaths per year as a result of collisions. Surprisingly, the deadliest buildings to birds are low-rises—buildings that are 4 to 11 stories tall. Collisions with these medium-sized buildings kill about 339 million total birds per year. And even though they reach farther into the sky than either residences or low-rises, high-rises (buildings taller than 11 stories) only account for about 508,000 bird deaths each year.

In addition to numbers of birds killed by collisions, the study identifies three bird groups (including hummingbirds, swifts, and warblers) and six migratory species listed by the U.S. Fish & Wildlife Service (USFWS) as Birds of Conservation Concern that are highly vulnerable to building collisions: Golden-winged Warbler, Painted Bunting, Canada Warbler, Wood Thrush, Kentucky Warbler, and Worm-eating Warbler. “Comparing the total numbers of birds killed is useful for getting a rough idea of the magnitude of a threat, but identifying which species and regions are most vulnerable is also crucial for implementing conservation policy and management actions,” Loss says.

The researchers found that, on a per-building basis, bird collisions with individual residences in rural areas kill more birds than collisions with individual residences in urban areas, but that cumulatively, bird collisions with urban residences kill more birds than collisions with rural residences. This is because there are far more total urban residences in the U.S. What’s more, the larger buildings in urban areas (for example, skyscrapers in cities and low-rises on office and university campuses) kill more total birds on average than residences.

Much of the data used in this study is from surveys and collections done east of the Mississippi River and during migration, and from collections mostly done in large cities that have collision-monitoring programs. The researchers expressed a need for more research at a wider variety of low-rise building types and across all seasons to help improve estimates of bird deaths. They also called for more research in the western U.S. to explore possible geographical differences in per-building bird deaths and to better assess whether any western bird species are particularly vulnerable to collisions with buildings.

People can help researchers learn more about how many birds die from collisions with buildings by assisting with a collision-monitoring program—or by starting one. Many such programs are sponsored by local birding groups such as regional Audubon Societies. According to other research, people can help reduce the number of birds killed by collisions with their homes by placing decals close together (within 5–10 cm of each other) on windows or locating bird feeders within 1 meter of windows so that birds have less momentum after taking off from the feeder if they do hit a window. For larger buildings such as low-rises and high-rises, research has shown that turning off lights at night reduces collision rates. “Many birds migrate at night and bright lights disorient and attract them,” Loss says. “Birds either immediately collide with lighted buildings, or they become entrapped in the mazes of windows at street-level until they tire out or die from colliding with windows.”

Read the article, “Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability,” online. The research project was supported by the Smithsonian Migratory Bird Center and the U.S. Fish and Wildlife Service.


Contact: Sean Hubbard (Agricultural Communications Specialist, Oklahoma State University),, (405) 744-4490

About the Journal: The Condor began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society ( The Condor has developed into one of the world’s foremost ornithological journals.