Colonial Waterbird Nesting Sites
Click the colony locations below to learn the colony name. Clicking a location shows the colony name and breeding species. Click through the pop-ups to see the years when there was nesting activity for each species.
2019 Season Highlights
During the 2019 breeding season (February-August), 84 dedicated SFBBO volunteers spent 835 hours monitoring a total of 50 potential waterbird colonies across 49 sites, 49 of which became active breeding colonies. We monitored 18 gull, tern and shorebird colonies and 31 heron, egret and cormorant colonies.
Figure 1. Map of 2019 Colonial Waterbird colonies and peak nest counts in San Francisco Bay, CA. Circle sizes indicate peak nest counts for our target species groups. Counts are based on observational methods, and do not include data collected during California Gull walkthroughs.
In 2019 our volunteers monitored:
87 American Avocet nests
23 Black Skimmer nest
5 Black-necked Stilt nests
22,513 California Gull nests
90 Caspian Tern nests
1 Elegant Tern nest
877 Forster's Tern nests
239 Black-crowned Night Heron nests
407 Double-crested Cormorant nests
135 Great Blue Heron nests
156 Great Egret nests
3 Green Heron nests
331 Snowy Egret nests
Photo by Tom Grey
California Gulls are the most abundant nesting waterbird in the South San Francisco Bay and SFBBO has been monitoring the growth of the breeding population since 1980. In 2019, SFBBO monitored 10 California Gull colonies via walkthrough surveys from May 12–25. These 10 colonies encompass all known South Bay breeding locations of this species.
Figure 3. Percentage of breeding California Gulls within each colony site, 1980-2019, South San Francisco Bay, CA. PAFCB = Palo Alto Flood Control Basin. Alviso A6 provided dry habitat suitable for nesting gulls until 2010 when the levees were breached and the site was opened to tidal action. Following the loss of Alviso A6 as suitable nesting habitat, gulls redistributed to other nesting sites in the South Bay.
Please reference our Annual Report for complete data and descriptions. For reports from this year and previous years, please visit https://www.sfbbo.org/colonial-waterbird-monitoring.html