A few places in eastern North America — Cape May, New Jersey; Taddousac Dunes, Quebec; and Lake Pontchartrain, Louisiana — are well known spots for witnessing “morning flight” — a phenomenon in which mostly nocturnal birds continue migrating into the daylight hours. It’s a thrilling sight to behold, even if it’s quite challenging to identify the birds as they fly by.
A few years ago, birders in California located a similar morning flight location just west of the Bear Divide Vista picnic area in the San Gabriel Mountains in Los Angeles County.
Birds that are flying north or northwest over the Los Angeles basin encounter the San Gabriel Mountains and must either cross or attempt to go around them. If these birds follow the base of the mountains, Bear Divide is the first low pass they encounter. The divide is at 1,686 feet above sea level while the surrounding mountains reach 2,690 feet. The broad, low base of the two canyons that feed into Bear Divide, combined with the narrow and steep topography, likely contributes to the large numbers of migrating birds that can be observed at the site.
In 2019 and 2020, researchers from Occidental College, UCLA, the Cornell Lab of Ornithology, and other groups used regular counts to quantify the numbers and identities of birds migrating through the area. They tallied almost 45,000 birds during the first two springs, counting from late March to late May. They began about 15 minutes before sunrise and wrapped up between 8:30 and 10 a.m. most days.
The Moore Lab of Zoology at Occidental College continued the count in 2021 and plans to again this year. The team needs donations to the project and help from volunteer counters. See the Bear Divide Migration Count website for more info.
To learn more about the site, read this paper in the journal Western Birds.