No matter where you live in the Bay Area, you’ve likely noticed the sinewy, graceful forms of great blue herons and great and snowy egrets. These sylphlike birds are mostly solitary, whether flying overhead or braced in stillness for the hunt. But during the springtime breeding season, they congregate in noisy colonies to nest and rear their young.
Heron and egret breeding colonies, or heronries, are widely distributed throughout the Bay Area. In collaboration with the San Francisco Bay Bird Observatory, the Audubon Canyon Ranch recently released a comprehensive heron and egret breeding atlas for the region. The atlas summarizes the monitoring efforts conducted by the two groups over the last 37 years and documents the exact locations of colonies in the region.
John P. Kelly, director of the Cypress Grove Research Center at Audubon Canyon Ranch and lead author of the atlas, says the best time to visit colonies is May and June. Any earlier and you may scare the birds off their nests, exposing the eggs or young to predation by crows and ravens. He recommends approaching a colony cautiously. If you observe any “alert” behavior such as alarm calls, head-lifting, or birds flushing from their nests, you should back off.
There are many accessible colonies throughout the Bay Area, starting with Audubon Canyon Ranch’s Bolinas Lagoon Preserve, one of the largest breeding colonies on the West Coast. The 2007 viewing season there runs from March 17 to July 15 (open weekends 10 a.m. to 4 p.m., weekdays by appointment). Farther inland, Kelly recommends the downtown Santa Rosa colony of up to 100 snowy egrets and 250 black-crowned night herons that set up camp in a stand of eucalyptus in a median strip on West Ninth Street at Simpson.
In the South Bay, go to Vasona County Park in Los Gatos, where great blue herons breed in a grove of eucalyptus trees directly above a trail adjacent to the children,s playground. Heron enthusiast Linda Sullivan is often there with her scope. She also hosts a blog (with great pictures) at www.okaponds.com. In the East Bay, check out Lake Merritt, where snowy egrets and night herons nest on the islands at the lake’s northern edge, or go to Hayward’s Ruus Park, at the corner of Folsom and Tampa streets, where you,re sure to see up to 100 great egrets in the eucalyptus. In San Francisco, head over to Golden Gate Park, where half a dozen great blues nest at Stowe Lake; find out more at www.sfnature.org.
You can download a free copy of the heron and egret atlas at www.egret.org/atlas.html. To learn more about herons and egrets, join John Kelly on Thursday, May 17, at PRBO Conservation Science in Petaluma. Call PRBO at (707)781-2555, ext. 307, for details.