The birds are still warm to the touch when Nick Lund lifts them from the cold sidewalk. There is a common yellowthroat, its neck a dusty yellow, and a white-throated sparrow, sleeker than the house sparrows that are so common around here.

With their wings folded and their spindly legs pulled up underneath them, they look as if they are perching. But they are both dead, killed by, of all things, the Thurgood Marshall Federal Judiciary Building near Union Station.

Nick slips the tiny bodies into a plastic bag and marks it with the date and location. We start walking west. Sunrise is coming, and there’s a lot of ground to cover.

“You usually find them next to the building,” Nick explains. “They hit, and they drop.” Neotropical songbirds migrate twice a year through our region: heading north in the spring and back south in the fall to their wintering grounds in Central and South America.

Warblers, sparrows, thrushes and other species have been doing it for thousands of years. In the last hundred or so, humans have put tall buildings in their way. The birds fly at night when it’s cooler and to avoid predators, only to slam into buildings that dazzle them with their lights or whose glass-covered walls appear invisible in the murk.

Nick Lund is a volunteer with Lights Out for Birds, a group whose members walk D.C. neighborhoods early in the morning during migration season to collect birds that have died from striking buildings. Nick photographs his collected birds from the mornings walk. (John Kelly/The Washington Post)

The result is an avian death toll that some experts say is second only to habitat destruction when it comes to killing birds. Estimates range from 300 million to a billion birds killed annually in North America from striking buildings.

“Most of the little guys don’t stand a chance,” Nick says. “There’s no weight to them, nothing of substance to protect them.”

Nick is among volunteers with a group called Lights Out for Birds that is trying to determine exactly how many birds are killed in Washington. Starting about 5:30 a.m. during migration season, they head out. Nick takes Wednesdays, hiking from Union Station, up Massachusetts Avenue NW, looping past the Convention Center and then into Chinatown. Other volunteers walk a route in Foggy Bottom. They don’t find dead birds every morning, but when they do, they collect them, noting the details of their demise. The corpses are given to the Smithsonian.

“It’s a cool way to see the city,” Nick says. Most of Washington is still asleep. As we walk — at a brisk pace, our eyes sweeping the ground in front of us — the homeless are still abed, cocooned in doorways. Prostitutes are just finishing their work nights, and hard-hatted construction workers are just starting their work days.

“Is that a bird?” Nick says as we cross North Capitol Street, headed west. “No, it’s some newspaper.”

It’s a job that has to be done early. When the sun rises, crows and seagulls swoop in and carry away the evidence, or building managers hose it into the gutter.

Nick, 30, isn’t an ornithologist. He’s a lawyer with the National Parks Conservation Association. He dates his interest in birds to the moment he was standing in a used bookstore, flipping through a birding field guide, and something came over him. It was the realization that birds were emissaries from the natural world and that they are all around us.

“A lot of birders have that,” he says. “A switch goes off.”

Not all the birds we find are dead. Some are merely stunned. At 300 New Jersey Ave. NW, we encounter a swamp sparrow on the ground. It resists Nick’s effort to scoop him into a paper bag, then flutters under an overhang.

“He can fly,” Nick says. “That’s probably a good place for him to be, under that ledge.”

This is Nick’s second year volunteering for Lights Out. He knows the worst places for birds. Thurgood Marshall is bad. It has a glass-enclosed, tree-filled atrium. You can just imagine the birds looking for refuge in the branches only to collide with the glass.

The worst is TechWorld Plaza at Ninth and Massachusetts NW, where the Renaissance Washington hotel is. The exterior is made of smoky glass, and about six stories up is a skywalk that runs between the two halves of the complex.

“You could draw a circle 10 feet around on either side of where the skywalk joins the building and that’s where you’d find them,” Nick says.

Lights Out works with building managers, encouraging them to turn off the lights at night. (The Thurgood Marshall building does that now, which seems to have helped a little.) The organization tries to persuade architects not to use so much glass, or if they must, to mark it in such a way that it’s visible to birds.

“I think it’s clichéd these days to have a glass-covered building,” Nick says. “Try something else!”

It’s nearly 7, and the early-morning dogwalkers are out now. We turn off Fourth Street onto I Street. “There’s one,” Nick says. In front of 425 I St. NW, a common yellowthroat cools on the red-brick sidewalk.

Nick pulls another plastic bag from his backpack.

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