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Collisions with buildings kill 365-988 million birds annually

A bird left this trace after colliding with a window. Photo by Alan Hensel, Wikimedia Commons.
A bird left this trace after colliding with a window. Photo by Alan Hensel, Wikimedia Commons.

For years, it has been assumed that a staggering number of birds die in collisions with buildings in the United States — between 100 million and one billion every year. The total is often cited as fact, even though it was presented, in 1990, as only a rough estimate. Now, thanks to a systematic review of published studies and unpublished collision-monitoring datasets, we know not only that the estimate is true, but also that low-rise buildings and residences kill more birds than skyscrapers. What’s more, mortality caused by building collisions may be having an effect on populations of vulnerable species. Between 365 and 988 million birds are killed annually by building collisions in the U.S., say researchers Scott R. Loss, Sara S. Loss, and Peter P. Marra of the Smithsonian Migratory Bird Center and Tom Will of U.S. Fish and Wildlife Service’s Division of Migratory Birds.

“Our results support the conclusion that building collision mortality is one of the top sources of direct anthropogenic mortality of birds in the U.S.,” they conclude. “Among other national estimates that are data-driven and systematically derived, only predation by free-ranging domestic cats is estimated to cause a greater amount of mortality.”

Canadian and U.S. studies agree: Cats are the most lethal threat to birds.

Collisions with buildings between 4 and 11 stories tall account for roughly 56 percent of overall mortality (339 million deaths, on average), say the analysts. Residences — detached houses and multi-unit residences 1-3 stories tall — account for 44 percent (253 million), while high-rises, buildings at least 12 stories tall, cause less than one percent (508,000).

Residences kill birds at a lower rate than high-rises — 2.1 vs. 24.3 birds per skyscraper — but residences vastly outnumber high-rises. The findings suggest that reducing mortality substantially will require mitigation measures to be applied across a huge number of structures.

Loss, Loss, Will, and Mara found that six species that have been listed as national Birds of Conservation Concern due to their declining populations are highly vulnerable to building collisions: Golden-winged Warbler, Painted Bunting, Canada Warbler, Wood Thrush, Kentucky Warbler, and Worm-eating Warbler.


The researchers published their findings in early January 2014 in The Condor: Ornithological Applications, the journal of the Cooper Ornithological Society.

Read the paper

Scott R. Loss, Tom Will, Sara S. Loss, and Peter P. Marra (2014) Bird–building collisions in the United States: Estimates of annual mortality and species vulnerability. The Condor: February 2014, Vol. 116, No. 1, pp. 8-23.

A version of this article appears in the April 2014 issue of BirdWatching. Subscribe.

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