No, your eyes aren’t playing tricks on you. That will really be thousands of birds overhead tonight and you may want to keep your lights off for the occasion.

As many as 29,000 birds are expected to fly over the Baltimore area, according to data from Washington College. Almost 10,000 will fly over Columbia.

Humans, thousands and thousands of years ago, traveled along what today is I-95 for warmth, said Maren Gimpel, associate director of Foreman’s Branch Bird Observatory at Washington College’s Center for Environment and Society. Birds have taken the route — known as the Atlantic Flyway — long before the highway was here.

It’s the safest, most convenient path for them. It’s east of the mountains. It’s close to the shore, where the weather conditions suit them, but not too near the sea that strong winds could take them. They fly at night with a gentle tail wind to help push them along. If it’s too windy, it becomes too burdensome to control the flight.

The sky needs to be clear as well. Birds follow the stars and the moon to navigate to their wintering grounds. Some will land just as the climate gets a little warmer, such as in South Carolina or Florida. A bulk of birds will venture to the Caribbean and Central America. Only some species will trek further south, reaching Brazil and Venezuela. Light pollution can disorient the birds and collisions are common during migration (The U.S. Fish and Wildlife Service estimates that one billion birds smash against windows every year). Artificial lights prevent birds from interpreting stars correctly.

Volunteers with Lights Out Baltimore, a program that’s part of the Baltimore Bird Club, rescue injured birds from window collisions during fall and spring migration. The first two weeks of October tend to have a migration boom, said Lindsay Jacks, who heads the program.

Jacks is encouraging people to turn off the lights if they can, or close the curtains if they must be kept on. For businesses that are over 20 stories tall, she encourages owners to only keep the lights on when employees are on the floors.

Birds can also collide with windows if they see trees or an open sky in the reflection. Marking the glass with soap and scuffing it can help the bird realize there is a physical barrier.

A lot of sparrows are making their way during peak migration, Jacks said. Species travel in turns, she said. Later on in the migration season, which usually starts in August and ends in November, American woodcocks will flock through.

Jacks also said if a bird is hanging out near a building downtown and it’s not flying away when approached, it needs help.

“The best thing to do would be to contain it, if the possible, into a paper bag,” Jacks said. “You can close the paper bag, fold it down one time, and put a clothes pin or a paper clip or a binder clip.”

After that, it’s best to contact the closest wildlife rehabilitator.

Birds will fly through the night, Gimpel said. As the sun rises, the birds will likely check for green spaces, like Patterson Park, to rest and refuel. They may stay over the Baltimore area for a couple of days, depending on how much energy they used to get here and the weather. Hurricanes Helene and Milton will likely affect their flight pattern.

Gimpel said researchers have been monitoring fall migration for decades. They placed mist nets — very fine mesh strung up between two poles — near the building, which is nestled in a waterfront refuge. Birds can’t see the mesh, so they fly into it. The birds fall in the nets, which sort of resemble old sailing ships with hammocks. Staff untangle them, pick them up and bring them to the observatory.

There, they measure their wing length, determine their sex and check their body for fat, looking for yellowish lumps under the bird’s wings and the base of the belly. Fat is crucial for them to be able to fly long distances, sometimes hundreds of miles at a time.

Then, they give the bird a uniquely numbered band to help researchers track migration, so they can estimate how many are expected to fly over. Bird population has been dropping. It’s important to understand why, she said, and by how much.

“I know for so many environmental issues, so many people feel like there are big problems and there’s nothing much we can do to make a difference,” she said. “Honestly, like, just turn off your light. Your electric bill goes lower, and you’re just gonna make it like a little bit easier for these birds that are, you know, making these epic journeys.”