SFBBO's Colonial Waterbird Report Relaunches Bigger Than Ever!

By Science Director Dr. Nathan Van Schmidt

​For over four decades, SFBBO's Colonial Waterbird Program has sent trained volunteers into the field each spring and summer to watch over the Bay Area's nesting herons, egrets, cormorants, terns, and gulls. Our annual monitoring report has long been a cornerstone of that effort, combining all the data gathered by our hard-working volunteers on how these majestic birds are faring across the region. In 2020, we undertook a major overhaul of our monitoring protocols to streamline the monitoring protocol. That broke all our old analysis code, and the report went kaput. But that was well worth it for the on-the-ground tradeoff: new volunteers could be onboarded more easily, and more people than ever could participate in avian science! ​And did it ever grow substantially. In 2024, Audubon Canyon Ranch ended their long-running sister monitoring program in the North Bay, and we were able to step in and take the 44 colonies in Marin, Sonoma, Napa, and northern Contra Costa counties under our wing (pardon the pun). That scientific rescue effort required another two years of building relationships, training volunteers, and figuring out logistics before we were ready to publish again. But I’m thrilled to say: the report is back!

​Spearheaded by Amy Parsons, SFBBO’s Lead Waterbird Biologist, the new 2025 Colonial Waterbird Monitoring Report summarizes what our community scientists found across 76 active nesting colonies across 82 sites spanning from northern Napa Valley to Santa Cruz. Our monitors documented 2,741 heron, egret, and cormorant nests and 747 tern and shorebird nests—with Double-crested Cormorants as the most abundant nesting species. Some of these rookeries were impressively huge: Dover Park hosted over 250 nests of Snowy Egrets and Black-crowned Night-Herons, and the Alviso pond complex continued to support large concentrations of cormorants, terns, and shorebirds. 

​Behind the scenes, we also developed a new mathematical algorithm to estimate fledgling production from our simplified field protocols. For the first time, we can say that the huge Great Egret colony at Gold Hill produced an estimated 284 fledglings! Because our volunteers can't follow individual nests through their entire lifecycle, we needed a way to correct for double-counting slow-developing chicks on consecutive visits and account for nests hidden by foliage that we know are there but can't always see. The result is a more rigorous estimate of breeding success that we can apply consistently across all our sites going forward, strengthening the scientific value of the dataset even as we've made fieldwork more accessible. Those key measures are going out to both federal agencies like the U.S. Fish and Wildlife Service and local ones like Santa Clara County Parks to help guide their conservation of these keystone birds and their habitats.

​One of the report's most significant stories is about California Gulls, a species that has a reputation of being a management headache in the South Bay for their tendency to predate nests of threatened birds like Snowy Plovers. But here's where it gets complicated: did you know California Gulls were once also listed by the state as a bird of conservation concern? Their native breeding grounds are at Mono Lake, a salt lake with specialized habitat that they need, and which has long been threatened by unsustainable water withdrawals to Los Angeles. It wasn’t until a few decades back when they were delisted because of the explosive growth of the San Francisco Bay population and an apparent stabilization of Mono Lake’s water levels. But with Mono Lake plagued by continuing water overdraft that has driven collapses in invertebrate prey, our partner scientists there reported 2024 had the lowest-ever count (just 20,258 birds) with chick production collapsing by 97%. Back here in the Bay, our walkthrough surveys found 36,820 breeding adults across 9 colonies in 2025, a 9% decline from the previous year and part of a broader years-long plateau.

​Our local population may represent over 60% of the entire state's breeding birds and roughly 10% of the global population. With South Bay now supporting more breeding California Gulls than Mono Lake, it is a potentially important refugia for California Gulls, even as they pose a risk to the nests of Forster's Tern, American Avocet, and other sensitive waterbirds. Land managers face the genuinely difficult task of protecting rare shorebirds from gull predation while recognizing that the Bay Area may be this species' most stable breeding ground in all of California. There are no easy answers, but in May we will get in our kayaks to head back out to the gull colonies to continue gathering the long-term data needed to navigate this tricky situation. 

​None of this would be possible without our extraordinary community scientists. In 2025, 118 volunteers contributed over 1,000 hours. That’s equivalent to more than $40,000 in donated labor! They spent their weekends peering through spotting scopes, counting nests, recording disturbances, and building the kind of long-term dataset that no single research team could maintain alone. To every one of you: thank you!!

And now we're gearing up for what promises to be our biggest season yet. The 2026 nesting season launches in earnest, with over 100 volunteers trained and ready to head into the field. It's the largest monitoring effort in the program's history. That said, we still have a few colony sites in the North Bay that need dedicated monitors. If you or a birder you know in Marin, Sonoma, or Napa County would like to contribute to real conservation science while getting to know your local waterbirds intimately (or if you’re in South Bay and want to join us for California Gull Walkthroughs in May) just email Amy to get involved!