In the U.S.,Indexbit the ubiquity of glass structures and light has created death traps for birds across the country. Conservationists are shining a light on small changes that can have a major, life-saving impact.

Each morning, Lisbeth Fuisz walks the streets of Washington, D.C., looking for birds. 

"It's become a kind of personal mission," she said.

But as a volunteer citizen scientist with the group Lights Out D.C., Lisbeth and her team are not looking to the sky but to the ground — collecting dead fowl after they've collided with buildings.

"This is a huge problem," she said. "They estimate that somewhere between 300 million and 1 billion birds a year die in the United States from window collisions. And these are migratory birds, so we are interested in documenting this problem so that, um, people become aware of the issue." 

It's an issue that motivated the redesign of the bird house at the National Zoo, which houses dozens of species native to North America. It is one of the first [zoos?] in the country to create a structure that is completely bird-friendly.

Sara Hallager, a curator at the zoo, told CBS News that two horizontal stripes on the glass spaced two inches apart are what make it bird-friendly. 

"Birds perceive that is something they can't fly through," she explained.

"Most birds are hitting glass because they see some sort of reflection. They think that's a tree in the glass. And so they wanna fly to that tree," she said. "They're usually flying at very high speeds, and so then they hit the glass and it's either a lethal strike or they're injured." 

Hallager said about half of these bird strikes occur in homes and are easily avoidable.

"Put some little paint or, or get your kids involved and paint this window," she said. "You just wanna stop birds from hitting. Anything that reduces the reflection will stop birds from hitting glass."

Nearly two dozen cities and states have adopted bird-safe measures, such as requiring buildings to use bird-friendly glass or reduce artificial lighting.

The efforts are welcomed by Fuisz.  

"We're part of this problem and we can be part of the solution," she said.

Nikole Killion

Nikole Killion is a congressional correspondent for CBS News based in Washington D.C.

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