The bottle-green waters of Lagunitas Creek linger at White House Pool, where the tidal inlet forms a thin elbow of a lagoon that runs parallel to Sir Francis Drake Boulevard and on past town. Languid as a lazy river, the soft turn in the creek lays out a bucolic scene: tall grass, toasted a soft cinnamon by the sun, edges the shore, while blackberry brambles tangle along the steep soil bank above the water. Surrounded by 22 acres of wetlands, White House Pool is an eden for the flora and fauna that make up the dense biodiversity of Tomales Bay. Orchestral birdsong is only occasionally interrupted by the din of a passing car.
But close observers—and a new scientific report—describe a changing scene.
Keith Hansen, an artist and bird illustrator from Bolinas, has returned to this quiet recess for 30 years during the Christmas Bird Count, an annual census performed every winter by volunteers in the Western Hemisphere. Its purpose is to provide population data to help guide conservation biology. The edges of White House Pool mark the southern boundary of Mr. Hansen’s “count circle.” From there, he charts a course north along the water, walking five into Inverness, recording every bird he sees as he goes.
“One year, we ended up seeing 109 species of birds just walking along the road,” he said. “That’s kind of incredible, to see a 10th of all of North American bird species in one day.”
Enough time spent birdwatching along the shores of Tomales Bay can reveal sights so idyllic they can feel feigned, as if the estuary had somehow been spared the creeping blight of a changing climate. It takes the long perspective of someone like Mr. Hansen to know otherwise. He’s aware that things are not all well and good for his beloved birds, especially those that live on the water, like bay ducks.
“It seems like their numbers have gone down,” he said. “You used to see coots and stuff almost every year, but now we hardly ever get them.”
Research conducted by Audubon Canyon Ranch and published in May by The Waterbird Society described the extent of the decline in wintering waterbirds on Tomales Bay, signaling a bleak outlook for their future. The study, a product of the last 30 years of an ongoing monitoring program, found that average wintering waterbird numbers have decreased nearly 12 percent since 1992. Meanwhile, the study notes, the total number of breeding birds in North America have decreased nearly 30 percent since 1970.
“I do believe that waterbirds are our canaries in the coal mine, and that they’re telling us about what is going on in the environment,” said Nils Warnock, the director of conservation science at Audubon Canyon Ranch and the study’s lead author. “Right now, they’re telling us that there’s a fair amount of negative things going on.”
Changing ocean conditions are one of the variables influencing winter waterbird populations, the study found. Water temperature and the amount of offshore upwelling—a process by which cool, nutrient-dense water rises to the surface—are factors that dictate the biomass of herring, a forage fish whose eggs make up one of the main food sources for Tomales Bay waterbirds. Historically, local herring runs took place consistently throughout the winter, fattening up different types of waterfowl and giving them the necessary energy for northern migrations and egg-laying.
“In winter, a big successful herring run translates to more birds being produced in the Arctic, which is great,” said Josiah Clark, a consulting ecologist who runs a habitat restoration business in San Francisco called Habitat Potential. “You could almost set your watch to them, but now everyone is just shrugging their shoulders.”
Herring lay their eggs in eelgrass, a straight, weed-like plant common to many estuaries. Tomales Bay supports one of the largest concentrations of eelgrass left in California, its underwater meadows combed back and forth by the tide. The brant, a small, dark goose, tends to flock to eelgrass beds in the winter, where they feed. Yet the Audubon Canyon Ranch study found that their wintering populations have also significantly slumped.
While fluctuations in eelgrass availability can threaten brants, Dr. Warnock sees global climate change impacts as a driving force behind their disappearance from Tomales Bay. Researchers in Alaska who study brants have found that an increasing portion of the population is staying in Alaska over the winter. Warmer temperatures result in less sea ice, which allows the birds access to vast tracts of eelgrass beds on the Alaskan Peninsula.
“They’re just not coming down,” Dr. Warnock said. “But their population is also declining. In general, the world is not becoming an easier place for waterbirds, or any bird.”
Brants are also hunted in a reserve on Tomales Bay during certain parts of the waterfowl season, which runs from October through January.
In addition to brants, the study found concerning declines in Tomales Bay’s wintering surf scoter, black scoter, ruddy duck, American coot, western grebe, Clark’s grebe, gadwall, Pacific loon and common goldeneye. “I think it’s fair to say we’re having a massive population decline in all sorts of things,” Mr. Clark said.
Recently, this population decline has also included brown pelicans. Hundreds have washed ashore along Northern California’s coastlines this spring, their bodies malnourished and starved of food. While state officials and researchers grapple with potential causes, Mr. Clark stressed that brown pelicans shouldn’t be this far north at this time of year to begin with.
“They should all be in Southern California and Mexico breeding, so the fact that people are just talking about pelicans dying is really missing the point,” he said. “There are a lot more questions than answers.”
Despite the somber findings of the Audubon Canyon Ranch study, researchers did note immediate, if short-term, benefits for certain wintering birds from the Giacomini Wetlands restoration project. The National Park Service initiative restored around 200 acres of diked-off pasture lands at the southern end of Tomales Bay to tidal action in 2008. Dr. Warnock was quick to temper any excess optimism, however.
“It’s been favorable, but it still doesn’t offset something else that’s going on, which is probably more regional or global, like climate change,” he said.
For Mr. Hansen, who published an illustrated guide to the birds of Point Reyes last year, the growing scarcity of his subjects can be hard to bear in real time. It’s something he often talks about with his fellow birdwatchers.
“A lot of us think that in the past four or five years, there’s been a hyper-accelerated decline,” he said. “They’ve been declining, but it’s getting steeper.”