Cats' reputations have taken a hit in recent years as research has revealed just how many birds die at their furry paws.

A 2012 study by the University of Georgia and National Geographic found that U.S. cats could kill as many as 4 billion birds and small animals a year.

Similar research in New Zealand prompted a prominent economist to propose ridding the country of domestic cats.

But teeth and claws aren't the only threat to aviation populations.

Between 365 and 988 million birds die annually from crashing into windows in the U.S., according to a new report. Other estimates put that number as high as 1 billion.

Most bird collision deaths don't occur on skyscrapers but with the windows of smaller structures.

Buildings four to 11 stories high account for 56 percent of the deaths, according to an Oklahoma State University study. Residences account for 44 percent of bird collisions, and skyscrapers cause fewer than 1 percent.

A small building kills only a few birds a year compared with the 24 that die due to a single skyscraper, but the United States has 15.1 million low-rise structures and 122.9 million small homes but only 21,000 skyscrapers.

Researchers also found that certain species of birds are more vulnerable to deadly window collisions.

Anna's hummingbirds, black-throated blue warblers, ruby-throated hummingbirds, Townsend's solitaires and golden-winged warblers top the list.

How can we make glass less dangerous?

There are only a handful of groups actively testing ways to prevent birds from flying into glass.

Ornithologist Christine Sheppard oversees one at the Powdermill Avian Research Center in Rector, Penn.

Her research has shown that opaque stripes or dots covering just 5 percent of a glass surface can prevent 90 percent of collisions. However, the problem lies in getting people to use such glass.

Ornithologist Daniel Klem Jr. has been working to create no-crash glass for nearly 40 years, and he's had some success.

He found that birds — but not people — can see the short wavelengths that make up ultraviolet light. He theorized that window patterns that show up only in UV could deter birds while still giving people a clear view.

A chemist devised a UV film that dramatically reduced bird collisions based on Klem's research, but attempts to finance the project failed.

Still, other companies and research labs are testing and marketing UV-reflecting glass and decals, and some places even require buildings to meet particular bird-safety standards.

Minnesota structures that receive state funds must include certain bird-safety features in their plans, and since 2011, San Francisco buildings near parks or waterfronts must adhere to avian-safety requirements.

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