The Great Blue Heron nesting colony at DeSilva Island, in Marin County, California, is one of many colony sites that are monitored by Audubon Canyon Ranch (ACR) as part of its North Bay Heron and Egret Project. The Project was initiated in 1990 and reflects an ongoing effort to monitor the status of colonially nesting herons and egrets throughout five counties in the northern San Francisco Bay region.