Date: 9/16/25 6:50 pm From: Lance Benner via groups.io <lbenner...> Subject: [LACoBirds] American Crow and Common Raven Roost Site Survey
Hi Everyone, American Crows are gathering again in nocturnal roosts so Los Angeles Birders are restarting our community science American Crow and Common Raven Roost Site Survey for 2025-2026. Here's a recap of the email we posted last winter to announce this: Background information It's been known for many years that American Crows gather in roosts during the fall and winter in groups that can number into the tens of thousands. This has attracted considerable attention among researchers and birders in the eastern part of the country and numerous studies have appeared in the peer-reviewed scientific literature. This is also of interest for many Christmas Bird Counts. Some of the roost sites persist for decades but other last for much shorter intervals. Prior to settling for the night, crows often gather temporarily in "pre-roost" sites before moving on to much larger gatherings elsewhere. For example, last winter, American Crows appeared to be doing this on the east side of Hahamongna Park in Pasadena. Common ravens also assemble in large roosts in the winter; this was described in some detail in the book "Mind of the Raven" by University of Vermont biologist Bernd Heinrich. In southern California, the roosts haven't been studied very much, but we know informally about some locations, and strongly suspect that there are more. We are asking observers to post on the local listserves and/or email directly with information on large roosts of 100+ birds across the greater Los Angeles area. We welcome reports in Los Angeles and other nearby counties. Here's a summary of where we found crows and ravens last winter: American Crow: ==============Los Angeles County: Hansen Dam/Orcas Park Culver City: Carson Street near National Carson: Near 91 and Avalon Blvd Valencia: McBean/Valencia park-n-rideCastaic Lagoon Koreatown: Wilton Place Elementary School Orange County: San Joaquin Marsh. Thousands Saddleback College, Mission Viejo. 2500 during the 2024 CBC. Buena Park Library. ~500 Probably in the Anaheim Hills. Large numbers have been seen flying in the area. Ventura County: Simi Valley near Wood Ranch. Riverside County: Chino: Former roost, apparently decreased substantially by West Nile Virus years ago. Common Raven: =============Los Angeles County: Bronson Canyon Park: Hundreds gather there regularly. Sometimes there are 100-200 crows nearby as well. Debs Park Castaic Lagoon Antelope Valley: Possibly near 100th St. West, tamarisks ~1/2 mile north of Ave. A Or in other nearby trees? There were numerous ravens there at sunset on February 23. Possibly the dairy farm at 100th St E/Ave F. San Bernardino County: Palmetto and Marigold, Redlands: ~900 ravens on 2/15/2025 Goldstone DSS-14 at the Goldstone Deep Space Communications Complex Some of the questions we seek to answer are: Where do the birds gather to roost? How many birds? How long to individual roost sites persist? To what extent do roost sites vary over the course of a given fall and winter? One question that came up in the spring is West Nile Virus. Is anyone finding dead corvids at roost sites? We'll summarize reports episodically and then circulate a more comprehensive report in the spring when the birds have dispersed. Thank you! Regards, Lance Lance BennerPasadena, CA Community Science Chair Los Angeles Birders_._,_._,_
