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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 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. The primary goal of the Heron and Egret Project is to develop and apply
current and historical information on status of herons and egrets to wetland conservation
concerns in the San Francisco Bay area. Specifically, the project focuses on monitoring local and
regional trends in nesting abundance and reproductive performance (Kelly et al. 2006, 2007). A
brief summary of colony site locations and results is posted online at
The heronry at DeSilva Island is one of several colony sites in Marin County and is
known to have supported nesting herons and egrets since 1979 (Pratt 1983, Kelly et al. 2006).
The trees used for nesting are blue gum eucalyptus (Eucalyptus globulus) and are located along
the southern waterfront of the DeSilva Island town homes complex.
Condeso, T. E, and J. P. Kelly. 2016. 2016 Monitoring Results from the DeSilva Island Heronry: A report to the DeSilva Island Home Owners' Association. ACR Technical Report 90-3-38 © September 2016. Audubon Canyon Ranch, Cypress Grove Research Center, P. O. Box 808, Marshall, CA 94940.