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Buildings can be deadly obstacles for birds. Some 365 to 988 million birds are killed when they smash into structures, estimates a study published last month into The Condor: Ornithological Applications. The review went even further than a body count, though: The authors identified which species are most prone to collisions, and which types of buildings do the most harm.

The research, based on 92,000-plus records across 23 studies, is a “really good step” in increasing our understanding of building collision mortality, says Susan B. Elbin, director of conservation and science at the New York City ̽����ѡ. “We need to put the science behind this issue and not just tell the story of birds dying,” she says.

Previous figures were “pretty speculative” and based only on estimates, says lead author, Scott Loss of Oklahoma State University in Stillwater.

Towering skyscrapers might seem like the most obvious culprits, yet Loss’s team found that 56 percent of the mortality occurs at low-rises (4-11 stories tall); 44 percent at residences (1-3 stories tall), and less than 1 percent at high-rises (12 stories and up). The taller structures have higher per-building mortality rates, but residences are by far responsible for the most bird deaths due to their sheer numbers: The United States has about 129 million residences, compared to 21,000 skyscrapers.

When it comes to the kinds of birds taking a hit, neotropical songbirds that migrate long distances—like golden-winged warblers—are particularly vulnerable. That’s likely because they’re unfamiliar with their surroundings, says Loss, and drawn or disoriented by lights blazing at night.

���ܻ�ܲ��Dz�’s Lights Out program aims to remove the deadly attraction by working with building owners to flip off the switch at night during migration season. ���ܻ�ܲ��Dz�’s Elbin says that participants in New York, Toronto, and elsewhere have helped save thousands of bird lives a year—and had the extra perk of saving on their electricity bills.

Loss points out that that there are several ways to cut down on daytime collisions. Placing feeders closer to windows can help ensure that any birds startled by their reflection aren’t able to build up speed and harm themselves. Adorning windows with stickers, spaced 5 to 10 centimeters apart, or installing netting on the outside of glass, are additional ways to curb bird mortalities, he says.

The review, funded by the U.S. Fish and Wildlife Service, is just one piece of a larger study in collaboration with the Smithsonian Conservation Biology Institute, Loss says. The goal of the larger effort is to collect “more data and evidence-based estimates of bird mortality from different human causes and threats,” he says.

And threats there are aplenty. Kitties remain the number one killer: The group has found that , with feral felines mostly to blame.An additional , the group estimates. Next, they’ll investigate deaths related to power-line electrocutions and collisions, vehicle collisions, and possibly lead poisoning.

It’s a dangerous world for birds. But these kinds of studies will help shed light on ways to make it safer.