Executive Summary
The San Francisco Bay Bird Observatory (SFBBO) is a nonprofit organization dedicated to the conservation of birds and their habitats through science and outreach. The Colonial Waterbird Program (CWB) is one of SFBBO’s longest-standing community science programs, initiated in 1982 to monitor waterbird nesting colonies in the San Francisco Bay region. Over the past four decades the program has engaged hundreds of community scientists in waterbird nest-monitoring activities. Each year, trained community scientists repeatedly visit selected colonies to independently collect observational data on breeding abundance, behavior, timing, and success, as well as impacts of disturbance. Community scientists also assist SFBBO staff in conducting annual walkthrough nest counts at all known California Gull colonies in the South San Francisco Bay (South Bay). Together, these data are used to track changes in colony size over time and breeding success. This keystone dataset has informed many scientific publications (Jennings et al. 2024, Rauzon et al. 2019, Burns et al. 2018, Adkins et al. 2014, Pitkin & Woods 2011, Kelly et al. 2007, Kelly et al. 2006, Strong et al. 2004) and is used by landowners, resource agencies, and other conservation organizations to guide the conservation and management of colonial waterbirds.
In 2025, SFBBO community scientists and staff monitored 82 colonial waterbird colonies across the San Francisco Bay region, of which 76 had active nesting. Monitoring efforts documented 2,741 heron, egret, and cormorant nests across 72 active colonies, with Double-crested Cormorants being the most abundant species. The largest colony was at Alviso A5/A6/A7/A8 with 155 cormorant nests. We also monitored 6 active gull, tern, and shorebird colonies with 747 total nests, the largest being Alviso A16.
California Gull walkthrough surveys estimated 36,820 breeding adults across 9 colonies, a 9% decrease from the previous year. The South Bay population continues to represent a significant portion of the state’s breeding California Gulls, particularly as the Mono Lake colony faces ongoing challenges from drought and water management issues. This species was once listed as a species of special conservation concern by the State of California, and we argue that ongoing issues facing the species warrant reconsideration of the decision to delist it. We recommend that land managers carefully consider how to balance the impacts of this species on local Bay Area ecosystems with the significant declines it is facing elsewhere in California and take a cautious approach to its management.
A total of 118 community scientists contributed 1,020 volunteer hours to the CWB Program. This dedicated network of volunteers continues to make long-term waterbird monitoring possible across this expansive region. Many community scientists in the program develop relationships with landowners and communities living with the colonies, and both volunteers and staff lead presentations and bird viewings to educate community members about these birds and their needs for protection and management.