Collisions with low-rise buildings kill millions of birds each year

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

For years, it has been assumed in the United States that a staggering number of birds die in collisions with buildings – 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Now, thanks to a systematic review of published studies and unpublished collision-monitoring datasets, not only is that estimate true, but also that low-rise buildings and residences kill more birds than skyscrapers.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 of the Smithsonian Migratory Bird Center and U.S. Fish and Wildlife Service’s Division of Migratory Birds.

“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.”

Collisions with buildings 4-11 stories tall account for roughly 56 % 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 % (253 million), while high-rises, buildings at least 12 stories tall, cause less than 1 % (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.

This is not a problem restricted to North America, buildings and other man-made structures kill birds across the world and may reduce further populations of already threatened species. The report can be downloaded free of charge here

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