In a nondescript spot in the western Angeles National Forest known as Bear Divide, Ben Szanto on Tuesday, May 9, walked quickly, carrying in a cloth pouch a songbird he plucked from mesh nets that had been stretched across the mountainous ledge.
Szanto, 28, of Mar Vista, blew on the live bird’s feathers to uncover its muscle-to-fat ratio and placed it on a scale, as a team of scientists hurriedly jotted down physical traits. By quickly affixing a band with a unique serial number to the leg of this Swainson’s thrush, it’s forever coded with vitals and its migration spot — data that can be downloaded by the next person who finds the banded bird.
Where the mighty San Gabriel Mountains crouch down to only 1,500-foot elevation north of Lake View Terrace, thousands of migrating songbirds fly every day in the spring on their journey to Northern California, and some fly as far as Alaska. This recently discovered migration phenomenon has tickled the fancy of bird watchers and launched new scientific studies of bird migration in Los Angeles County.
“It is the ability to watch songbirds actively migrating which is really unique,” explained Ryan Terrill, assistant professor of biology at Cal State University, Stanislaus and science director at the Klamath Bird Observatory in Ashland, Oregon. The birds fly by in swarms like bees, dozens at a time, making Bear Divide the most amazing spot to watch migrating songbirds in California, experts said.
“If you see a dozen Western Tanagers, I’d say that was an awesome bird-watching day,” Terrill said during an interview on Monday, May 8. “Here, you can see 3,000 of them.”
Scientists didn’t even know that songbirds migrated during the day, he said. That changed in 2019 when Terrill heard about this place when he was doing post-doctorate work at Occidental College in Eagle Rock. He started visiting the spot in the forest to witness it himself. That led to an official bird-banding and bird-counting operation beginning in 2021 that continues today, staffed by graduate students from several colleges including Occidental, UCLA, Loyola Marymount, Cal State Los Angeles and Colorado State.
“It was very shocking,” Terrill said. “This is a really unique, weird and cool place and it is so close to Los Angeles. Holy cow! We couldn’t believe it.”
From Feb. 19 to May 11, trained observers counted 52,494 birds and 139 species, according to the Bear Divide Migration Count website. The numbers are off the charts. On some days, spotters counted as many as 20,000 birds, Terrill said. “With that volume of birds, it gives us a study pattern,” he said.
Beside biologists, everyday bird watchers are flocking there, said Chris Spurgeon, program manager with Pasadena Audubon Society. He will lead a special Mother’s Day bird walk to Bear Divide on May 14.
“On a day when there are a lot of birds moving through, you could see 100 times more birds than you’d see in any place in California,” Spurgeon said. “It is great for bird watchers.”
Lauren Hill, co-leader of the Bear Divide Banding Station, said on Tuesday that she enjoys sharing with everyday folks. It’s become a place where scientists and hikers merge.
“We met a couple last year and she was pregnant. They came back this year with their baby,” Hill said, as clouds began covering the mountain. The Swainson’s thrush was the last bird tagged on Tuesday. Like the other birds, it was released within a minute, she said. “With the kids, when they see us release the bird, you can tell it is a monumental moment.”
Some birds will get a tiny transmitter put on their back so land antennas can record their whereabouts, part of the Motus Wildlife Tracking System (Motus is Latin for movement).
There are 1,500 Motus listening stations in North America, most of them in the eastern U.S. Of those, 44 are in California, but only two are in Los Angeles County, Spurgeon said.
Pasadena Audubon received a permit from the U.S. Forest Service to place two antennas on an abandoned laundry building down the road from the Bear Divide Fire Station in November 2022, the first Motus device operating in the county. The group is hoping for an 80% reimbursement for its expenditures of about $9,000, from the Forest Service, Spurgeon said.
On Tuesday, Spurgeon flipped open the box that gets signals from passing birds that are wearing a transmitter. He punched the buttons to make sure it was working. So far, no birds have been detected, he said. That’s probably because so few birds have transmitters, since the program is so new in California, he said.
The other Motus station was installed April 3 and April 4 at the Los Angeles Zoo, the first in the city of Los Angeles, explained spokesman Carl Myers in an email. The zoo is collaborating with the Southern Sierra Research Station and Pasadena Audubon.
The L.A. Zoo station will be able to capture signals transmitted from birds flying in eastern Griffith Park, the Verdugo Hills, and south into East Los Angeles, Myers explained. “This is an important flyway path for birds migrating north to south and looking for low-lying routes among the mountainous landscape surrounding Los Angeles,” he wrote.
Knowing where birds fly to, where they stop for rest or for foraging, could help preserve bird migration sites, said Spurgeon.
“By having transmitters on the birds that fly past receiving stations, you get much more information about their precise movements,” he said. Scientists are learning that songbirds migrate in steps, stopping to eat and rest at points on their journey, like humans on a road trip. “Some of these are vital places that we need to protect,” he added.
Songbirds flying north found Bear Divide because it is the path of least resistance, being a low elevation spot in the 700,176-acre Angeles National Forest that forms the northern edge of Los Angeles County, Spurgeon said.
“If you are flying along a lower elevation spot, it makes it easier. At lower elevations, the birds don’t have to go up and over the mountains, especially the San Gabriels which are 7,000 to 10,000 feet high.”
No one knows exactly why small songbirds migrate during the day. Ornithologists once thought they only took to the air on their migration journey at nighttime.
“There’s a theory. Say they land somewhere in Los Angeles County, say in a parking lot of Trader Joe’s. They say, ‘I am going to take off and fly at dawn to find another resting spot,’ ” Spurgeon said. When they fly over Bear Divide, at lower elevation than other parts of the Angeles, they expend less energy, he explained.
The discovery of the songbird migration and the installation of Motus stations could signal a new understanding of smaller birds, researchers said. More Motus stations are proposed along the coast of California, said Spurgeon.
“Check back in a decade. We will have hundreds of transmission stations,” he said.
