State of the Estuary 2015: Wildlife Wintering Waterfowl Population Indicator

For dabbling ducks, we used the six most commonly observed species in the dataset: American wigeon, gadwall, green-winged teal, mallard, northern pintail, and northern shoveler. For diving ducks, we used the six most commonly observed “species”: bufflehead, canvasback, goldeneye (both Barrow’s and common goldeneye), ruddy duck, scoter (black, white-winged, and surf scoter), and scaup (lesser and greater scaup). Henceforth we will refer to the six diving duck taxa as “species.” Based on previous studies (Accurso 1992), birds coded as “goldeneye” were assumed to be predominantly common goldeneye, and birds coded as “scoters” were assumed to be predominantly surf scoters. For each group (dabbling ducks, diving ducks), the indicator developed synthesizes population change among all six “species,” rather than species by species. We used the historic period, 1989-1993, as the reference baseline from which we developed our benchmark. The reference period constituted the first five years of the time series available for analysis, and aligned with the published objectives of the San Francisco Bay Joint Venture. The most recent 5-year period (2010-2014) was compared to the reference baseline period. Abundance exceeding the reference value was scored “Good.” Abundance 40% or more below the reference baseline was scored “Poor.” Thus, Fair was 60% to 100% of the reference value. In addition, we calculated linear and quadratic trends for each group, in each region, during the entire period and also for the last 10 years.