Estuary News

December 2020

Tallying Bird Populations Then and Now

How many ducks and geese used the Estuary before the Gold Rush? The numbers are beyond conjecture, but they must have been mind-boggling. Observers writing about a hundred years ago noted major decreases during the era of market hunting, when waterfowl were shot to supply the restaurants and stores of California’s emerging cities, but offered no hard numbers. However, they recorded their observations of the abundance and seasonal presence of different species.

Since then, government surveys, Audubon Society Christmas Bird Counts, and sport hunting records show a mix of change and continuity, with some duck species either scarce or common in the last century and now, and other common species becoming rare or vice versa. The US Fish and Wildlife Service’s  (USFWS) Midwinter Waterfowl Survey has been the most authoritative source on the state of the Bay’s ducks, informing restoration planning.  But the survey may be in jeopardy due to shifting priorities and safety concerns; its loss would mean a return to the era of guesswork.

The closest we have to a pre-Gold Rush baseline are anecdotes like pioneer George Yount’s description of San Pablo Bay in 1854: “The wild geese and every species of water foul [sic] darkened the surface of every bay…When disturbed, they arose to fly the sound of their wings was like distant thunder…” In another mid-19th-century account, settlers complained of being “greatly annoyed by the almost deafening, tumultuous, and confused noises of the innumerable flocks of ducks and geese…at times blackening the very heavens with their increasing numbers.”

By the 1850s, those multitudes were already being reduced by commercial hunting. Before poultry and other livestock were raised for food in California, deer, elk, waterfowl, shorebirds, quail, even songbirds, turtles, and frogs were harvested for sale. One indicator of the impact of market hunting is the number of waterfowl sold in San Francisco: 300,000 in the 1911-12 season alone. The practice was banned in 1915, although “duckleggers” continued to operate for decades afterward. Three years after the ban, Joseph Grinnell, the first director of the University of California’s Museum of Vertebrate Zoology, wrote that waterfowl had “decreased by fully one-half during the past forty years.” Habitat loss also contributed, as tidal and freshwater wetlands were filled or converted to agricultural use.

Promotional postcard for duck hunting in 1915. Source: Publicity Commissioners of Alameda County

Grinnell and assistant curator Margaret Wythe co-authored Directory to the Birdlife of the San Francisco Bay Region (1927). Looking through my battered copy of the gray paperbound book, I’m struck by the incongruity between past and present statuses of some waterfowl species. White-winged scoter an “abundant winter visitor?” This duck’s presence in the Bay is now worthy of a Rare Bird Alert mention. Gadwall a “rare winter visitant” to a few North Bay marshes? It’s now a year-round Bay-wide resident.  Grinnell and Wythe reported wood ducks as “not known in a wild state in any part of the Bay region in recent years;” today they’ve made a remarkable comeback, nesting in most Bay Area counties, and aren’t hard to find if you know where to look.

Cavity nesters, wood ducks have responded to the placement of nest boxes. Not all human changes to the landscape have been bad for waterfowl: diving ducks like canvasback and scaup congregate in managed wetlands, and gadwall are partial to reservoirs. Canada geese, once present only in winter, now thrive year-round in Bay Area cities, grazing in urban parks, sports fields, and corporate campuses.

Christmas Count data from land-based observers and boat parties document some of these trends. A few years ago Bob Lewis of the Golden Gate Audubon Society analyzed numbers from the Oakland count circle between 1974 and 2011, comparing two 19-year periods to identify “winners and losers,” most of which jibe with my impressions from years as a local birder. The biggest loser, he found, was the white-winged scoter, with a 95 percent decrease. Numbers on recent Oakland counts have been in single digits, just one or two in some years. Northern pintail was down 90 percent, canvasback 65, red-breasted merganser 57. Conversely, the once-rare gadwall was among the top ten “winners,” along with common merganser, wood duck, cinnamon teal, and bufflehead.

White-winged scoter in British Columbia courtesy Ebird. Photo: Frank Lin.

The quietly elegant gadwall, in fact, has increased in numbers and expanded its range not just in the Bay Area but throughout North American and western Europe. The species nests later in the year than other dabbling ducks, reducing competition for nest sites and losses from predation, and its preference for islands as nesting habitat is a hedge against predation by land mammals. Wet seasons in its breeding grounds may also have boosted the population.

Midwinter Surveys rely mostly on aerial transects and use a somewhat different classification from the Audubon counts, grouping the three scoter species (surf, black, and white-winged) and the two scaup (greater and lesser) together because it’s hard to separate the species from the air. The surveys began in 1953, but US Geological Survey (USGS) biologist Susan De La Cruz says the quality of the data improved in the 1980s. In 2018, the total duck tally was 282,447, not including geese, swans, coots, and grebes.

De La Cruz cautions that year-to-year variations  in weather conditions and the timing of migration complicate interpreting short-term trends.  Some species are declining in the Estuary but stable or increasing in the Central Valley. One clear trend: scoters as a group showed a significant decline in the Estuary between 1981 and 2012. Factors may include mortality due to oil spills or fishery bycatch, contaminants in the mollusks they eat, or climate change—or they may be wintering farther north, in waters that aren’t surveyed. Scoter numbers were unusually high in 2018; whether that’s a hopeful sign or a fluke is anyone’s guess.

Midwinter Survey data can aid adaptive management by showing how wintering ducks respond when salt ponds become tidal marsh. For the 2015 State of the Estuary Report, Nadav Nur of Point Blue Conservation Science, Orien Richmond of USFWS, and De La Cruz examined trends for six species of diving ducks (like scoters) and six of dabbling ducks (like gadwall) in the North, Central, and South Bay areas, comparing 2010-2014 numbers with a 1989-1993 benchmark. While dabbling ducks increased in every region, diving ducks showed strong declines in the North and Central Bay and a small but not statistically significant increase in the South Bay. “Both dabblers and divers may be affected as managed ponds are converted to tidal marsh…” says the report. “Diving ducks will likely be more impacted whereas dabbling ducks can forage in shallow water within marshes, if these are present.” With migratory birds, though, local trends could reflect broader, even continent-wide changes in climate, habitat, and food resources.

Sandhill cranes at sunset. Photo: Rick Lewis

As important as it is to monitor duck populations as restoration proceeds, the Midwinter Survey has encountered some challenges. USFWS has shifted its priorities, focusing more on spring breeding area surveys, and concerns have been raised about the safety of low-level survey flights in urban areas. After having to skip 2019, federal biologists managed the 2020 survey with supplemental state funding. No survey is planned for 2021.

De La Cruz and other agency biologists had considered autonomous aircraft systems—drones—as an alternative to piloted aircraft. That effort was delayed when Interior Secretary David Bernhardt grounded his department’s drone fleet last January, citing “cybersecurity, technology, and domestic production concerns.” (National Public Radio reported that Interior had been using Chinese-manufactured drones.) Tests of new models meeting the department’s criteria are now under way, and there’s hope that a retooled survey can move forward.

Top Photo: Gadwall by Rick Lewis.

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