They steer by the stars, as their ancestors have done for generations. Hundreds of miles from their goal, they’re staking their lives on celestial navigation.

Suddenly, something bright and confusing looms across their path.

Then they slam into a skyscraper, a window, a radio tower. For these ill-fated birds, migrations are forever over.

“The birds are flying fast. They can’t stop,” said Keith Russell, assistant editor of “Birds of North America,” a major ornithology publication based here. “There’s no second chances.”

In Philadelphia and New York, Chicago and Toronto, songbirds are crashing into killer skyscrapers and towers.

In spectacular migratory disasters years ago, they smashed to their deaths against Philadelphia’s City Hall, the Washington Monument and the Empire State Building in New York.

Worse yet, experts say, those well-reported crashes into towers and skyscrapers are only part of the problem. The killing continues night and day, sometimes nearly at ground level, as birds slam into the windows of hundreds of homes in Philadelphia, its suburbs and New Jersey.

Most of these birds are songbirds — the same warblers, thrushes and vireos that sing near bird feeders or flash sudden glimpses of color between trees. The migratory singers pollinate plants, distribute seeds and eat millions of insects, but they are struggling to survive as development shrinks their woodland habitat.

“Both tall and small buildings have plenty of glass to deceive birds to death,” said Daniel Klem Jr., an ornithology professor at Muhlenberg College in Allentown, Pa., and a specialist on birds smashing into windows.

Windows prove deadly year-round, while crashes at skyscrapers and towers often happen in bad weather during spring or fall migrations.

The U.S. Fish and Wildlife Service is looking for ways to cut risks to songbirds here during those migration periods.

The plan is to identify brightly lighted skyscrapers “and try to get building owners to turn the lights off” during migration, said Flavia Rutkosky, the agency’s coordinator for the program. Similar steps are in place in Chicago and New Orleans.

Yet Klem and others say the problem and its solution aren’t that simple.

Nationwide, experts estimate that at least 100 million birds die by crashing into windows, buildings and towers every year, including songbird species such as warblers, which are already struggling to survive.

In the Philadelphia area, scientists are only beginning to investigate the extent of the deaths.

“It’s critical that we start now and get some benchmark data of what’s happening,” said Nate Rice, ornithology collection manager at the Academy of Natural Sciences. He and others have been studying avian smash-ups.

“The tallest buildings in the city may not be the biggest killers,” Rice said. “We’ll hopefully be able to show which buildings are a problem, why they are a problem and how we can mitigate the situation.”

So far, the problem has received little public attention here. Russell and others who have found dead birds believe most are quickly picked up, sometimes by city workers — or snatched by crows or other scavengers.

A spokeswoman for Philadelphia’s Center City District said, “There has never been a report of a dead bird found.”

“It just doesn’t happen,” was the initial reaction from Independence Blue Cross to Russell’s report of dead birds found outside its building.

A similar state of denial prevailed in New York before the Port Authority last fall agreed to a pilot program that uses nets to protect birds from crashing into the World Trade Center — and in Toronto before FLAP, the Fatal Light Awareness Program, convinced banks to cut their lights at night.

In Philadelphia, Rice said: “We’re not trying to single out tall buildings or tower owners and paint them as the bad guy. We’re just trying to work with them to understand the problem.”

Birds can be lured to death either by lights that destroy their ability to navigate, or by windows that show false glimpses of sky, trees or other features of the environment, experts say. The birds, deceived and disoriented, miss their flight path and are doomed.

Across the country, birds fly to their deaths against wires supporting radio and television towers at the rate of 4 million to 5 million a year. To meet the growing demand for cell phones and other devices, more towers are going up at a hectic pace. Veteran birder Chuck Hetzel is working with Rice to study deaths here.

Birds fly into windows as easily as a person might walk into an unmarked glass door, experts say.

“It’s more fundamental than getting killed by skyscrapers,” Klem said. “Wherever you have glass and birds in the same place, you have the prospect for this tragedy.”