Shorebirds

We used data from 101 randomly selected sites surveyed in 2006-2008 and 2021-2023 from around the San Francisco Bay (Wood et al. 2010, Reiter et al. 2011). We selected three species to represent each of the three body size/breeding latitudes sub-groups analyzed:

• American Avocet (Recurvirostra americana), Willet (Tringa semipalmata), and Marbled Godwit (Limosa fedoa) represented large-bodied, generally temperate breeding birds.
• Black-bellied Plover (Pluvialis squatorola) and Short- and Long-billed dowitchers (Limnodromus griseus, L. scolopaceus) represented medium-bodied, mid- to high-latitude breeding birds.
• Three species of the genus Calidris (Dunlin [Calidris alpina], Western Sandpiper [C. mauri], Least Sandpiper [C. minutilla]) represented small-bodied, high-latitude breeding birds.

We used statistical models to estimate the mean annual population density of these groups for each of three regions of San Francisco Bay (North, Central, and South Bay; as defined by Wood et al. (2010)). For the status analysis, our models compared densities during the baseline period (2006-2008 average) and the current reporting period (2021-2023 average). We used models to estimate long-term trends for each subgroup in each region based on 16 years of available data between 2006 and 2023.

For each of the nine sub-groups, we delineated benchmarks as the value 10% above or below the baseline shorebird density estimate (2006-2008 average), and whether or not the 95% confidence interval for current density estimates (2021-2023 average) overlapped the baseline density estimate. For example, the current mean density estimate for large shorebirds in the North Bay was more than 10% lower than the baseline density estimate for large shorebirds in the North Bay (suggesting a Poor score), but the 95% confidence interval of the current density estimate overlapped the baseline value, so we scored the status for this sub-group as Fair. We selected 2006-2008 as the baseline period because these years represented the state of shorebird populations just prior to a period of substantial change in wetlands in San Francisco Bay from large-scale restoration of saline ponds to tidal marshes.

Our approach to the trend score has changed since the 2015 report, to more closely align with the San Francisco Bay State of the Birds and to take advantage of more available years of data and a more statistically powerful method to track trends. We determined trend scores by evaluating significance of long-term trends (assuming 𝛼 = 0.05); if trends were not significant (i.e., P > 0.05), the trend was scored as No Change.

We determined the overall status and trend score for wintering shorebirds in the San Francisco Bay by tallying scores across the nine sub-groups and assigning the majority score.