Max Tarjan

Wilson’s and red-necked phalaropes (Phalaropus tricolor and P. lobatus, respectively), have
poorly understood conservation statuses. These species breed in northerly latitudes of North
America to migrate to staging areas at saline lakes in western North America, before migrating to
South American lands and waters. Given saline lake habitat is threatened worldwide by water
diversion and climate change, there is an urgent need to better understand phalarope population
and trends. We conducted coordinated monitoring of western North American staging areas of
historical importance to phalaropes: Great Salt Lake (Utah), Mono Lake (California), Lake Abert
(Oregon), Owens Lake (California), south San Francisco Bay (California), and Chaplin Lake
(Saskatchewan). We conducted surveys at each site during week-long “survey windows,” from
mid-July to mid-September, 2019 and 2020, with the goal of at least one survey per site per
window. Methods were standardized within sites but varied across sites, including plane-based,
boat-based, and land-based surveys. We report results from Great Salt Lake, Mono Lake, and
Lake Abert in 2019 and for all surveyed sites in 2020. The peak Wilson’s phalarope count from
all sites combined was 339,715 birds in 2019 (3 sites), and 126,288 birds in 2020 (6 sites).
Inclusion of unidentified birds in Wilson’s phalarope peak counts resulted in high counts of
370,811 birds in 2019 and 236,434 birds in 2020. The peak red-necked phalarope count from all
sites combined was 154,581 birds during 2019 (3 sites), and 53,762 in 2020 (6 sites). Inclusion
of unidentified birds in red-necked phalarope peak counts resulted in high counts of 291,643
birds in 2019 and 123,697 birds in 2020. The three additional sites monitored in 2020 added ≤1%
of the combined totals for each species/unidentified peak count. Timing of both species was
similar to historic patterns, with peak numbers in mid-July for Wilson’s phalaropes and in midto
late-August for red-necked phalaropes. Numbers of both species at Great Salt Lake
outnumbered those at other sites by an order of magnitude in 2019 and 2020. There is a need for
continuing standardization of survey methods across sites, research on phalarope movements
among sites and residence times at sites, and attention toward the issue of interpretation of
unidentified phalarope counts. Continued monitoring will help us understand phalarope
population trends, migratory patterns and timing, and response to climate and environmental
factors, and will provide a valuable indicator of the health of saline lake ecosystems.

Keywords

birds

waterbirds

population

Pond Complex

Alviso

Eden Landing

Ravenswood

Breeding Waterbird Populations Have Declined in South San Francisco Bay: An Assessment Over Two Decades

ariela — Tue, 28 Sep 2021 17:03:30 +0000

Breeding Waterbird Populations Have Declined in South San Francisco Bay: An Assessment Over Two Decades ariela Tue, 09/28/2021 - 10:03

Document Category

Scientific Reports

Author(s)

Date

2021-09

Summary

In south San Francisco Bay, former salt ponds now managed as wildlife habitat support large populations of breeding waterbirds. In 2006, the South Bay Salt Pond Restoration Project began the process of converting 50% to 90% of these managed pond habitats into tidal marsh. We compared American Avocet (Recurvirostra americana) and Black-necked Stilt (Himantopus mexicanus) abundance in south San Francisco Bay before (2001) and after approximately 1,300 ha of managed ponds were breached to tidal action to begin tidal marsh restoration (2019). Over the 18-year period, American Avocet abundance declined 13.5% (2,765 in 2001 vs. 2,391 in 2019), and Black-necked Stilt abundance declined 30.0% (1,184 in 2001 vs. 828 in 2019). Forster’s Tern (Sterna forsteri) abundance was 2,675 birds in 2019. In 2019, managed ponds accounted for only 25.8% of suitable habitats, yet contained 53.9%, 38.6%, and 65.6% American Avocet, Black-necked Stilt, and Forster’s Tern observations, respectively. Conversely, tidal marsh and tidal mudflats accounted for 42.9% of suitable habitats, yet contained only 18.4%, 10.3%, and 19.8% of American Avocet, Black-necked Stilt, and Forster’s Tern observations, respectively. Using a separate nest-monitoring data set, we found that nest abundance in south San Francisco Bay declined for all three species from 2005–2019. Average annual nest abundance during 2017–2019 declined 53%, 71%, and 36%, for American Avocets, Back-necked Stilts, and Forster’s Terns, respectively, compared to 2005–2007. Loss of island nesting habitat as a result of tidal marsh conversion and an increasing population of predatory California Gulls (Larus californicus) are two potential causes of these declines. All three species established nesting colonies on newly constructed islands within remaining managed ponds; however, these new colonies did not make up for the steep declines observed at other historical nesting sites. For future wetland restoration, retaining more managed ponds that contain islands suitable for nesting may help to limit further declines in breeding waterbird populations.

Hartman, C. A, Ackerman, J. T, Schacter, C. R, Herzog, M. P, Tarjan, L. M, Wang, Y., et al. (2021). Breeding Waterbird Populations Have Declined in South San Francisco Bay: An Assessment Over Two Decades. San Francisco Estuary and Watershed Science, 19(3). http://dx.doi.org/10.15447/sfews.2021v19iss3art4 Retrieved from https://escholarship.org/uc/item/16n259mc

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood