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.

2020 Season Highlights

 During the 2020 breeding season (February-August), 53 SFBBO community scientists contributed 395 volunteer hours monitoring a total of 40 active breeding colonies. We monitored 35 sites with active heron, egret, and cormorant colonies and 5 sites with active gull, tern and shorebird colonies. In 2020, SFBBO staff searched sites with inactive colonies for evidence of new breeding activity. There are 65 sites that historically had colonies and became inactive prior to 2020. SFBBO staff visited 38 of these sites, which comprised every known inactive colony with permissible access. ​

Figure 1. Map of colonial waterbird sites surveyed by SFBBO biologists and volunteers in 2020 in San Francisco Bay, CA. Sites in yellow contained breeding herons, egrets, and/or cormorants; sites in cyan contained breeding gulls, terns, and/or shorebirds; green sites were not surveyed or were surveyed before the peak breeding season (May-July); black sites were visited and no breeding activity was observed.

Figure 2. Locations of inactive colony sites scouted by SFBBO staff in 2020 in San Francisco Bay, CA. Locations in pink remained inactive in 2020; primary species that SFBBO targets for monitoring (Great Blue Herons or Double-crested Cormorants) were found breeding at purple locations; secondary species (Western Gulls), which are surveyed when they co-occur at colonies with primary species, were found breeding at the red location.

In 2020 our staff and volunteers monitored:

31 American Avocet nests
30 Black Skimmer nest
16 Black-necked Stilt nests
19 Caspian Tern nests
675 Forster's Tern nests
12 Least Tern nests
27 Western Gull nests
117 Black-crowned Night Heron nests
323 Double-crested Cormorant nests
130 Great Blue Heron nests
130 Great Egret nests
15 Green Heron nests
243 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 breeding population size since 1980.  In 2020, SFBBO, California Gull monitoring was suspended due to COVID-19.  SFBBO staff will resume surveys of all 10 breeding colonies in South San Francisco Bay in spring 2021.

Figure 3. Estimated number of breeding California Gulls in the South San Francisco Bay, CA from 1980-2019. 

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