Max Tarjan

South Bay Salt Pond Waterbird Surveys, September 2019 – February 2021

ariela — Wed, 19 Feb 2025 19:26:38 +0000

South Bay Salt Pond Waterbird Surveys, September 2019 – February 2021 ariela Wed, 02/19/2025 - 11:26

Document Category

Scientific Reports

Author(s)

Max Tarjan

Gabbie Burns

SFBBO

Date

2021-06

Summary

EXECUTIVE SUMMARY
This report serves as a data summary and coarse-scale assessment of waterbird and water quality monitoring efforts at six pond complexes in the South San Francisco Bay. Coyote Hills, Dumbarton, and Mowry salt ponds are owned by Don Edwards San Francisco Bay National Wildlife Refuge and managed for salt production by Cargill Salt. Alviso and Ravenswood complexes are owned and managed by Don Edwards San Francisco Bay National Wildlife Refuge. Eden Landing Ecological Reserve (Eden Landing) ponds are owned and managed by California Department of Fish and Wildlife (CDFW), with the exception pond CP3C, which is owned by Cargill Salt. This report is based primarily on data collected by the San Francisco Bay Bird Observatory between September 2019 and February 2021.

The purpose of this ongoing study is to describe avian use of ponds to guide regional waterbird conservation, management, and habitat restoration efforts. The South Bay Salt Pond Restoration Project (SBSPRP) is restoring over 15,000 acres of former salt evaporation ponds to a mix of tidal marsh and ponded wetland habitats. As the SBSPRP proceeds, understanding how waterbirds use ponds, identifying key habitat associations, and incorporating features essential to pond-dependent species into restoration plans will be increasingly important to maintain baseline numbers of waterbirds in the South Bay.

From September 2019 to February 2020, we conducted waterbird surveys and water quality sampling at 82 ponds (22 Cargill-managed salt production ponds and 60 SBSPRP managed ponds). Due to site access limitations associated with the COVID-19 pandemic, we surveyed 45 ponds across multiple complexes from March to April 11, 2020 and 25 ponds within Eden Landing Ecological Reserve from April 15 to May 2020 and December 2020 to February 2021. We examined species richness, abundance, and behavior of waterbird assemblages within and among pond complexes. We grouped species into guilds (e.g., dabbling ducks, diving ducks, gulls) based on foraging methods and prey requirements to understand waterbird use of these ponds. We also put these waterbird counts in the context of long-term trends to assess changes in waterbird numbers relative to baseline counts from before marsh restoration. We recorded 1,293,322 waterbird observations of 78 species (all sites combined). The Alviso and Eden Landing pond complexes supported the greatest species diversity and also the highest abundances of all complexes. The abundances of diving ducks, Ruddy ducks, dabbling ducks, and medium shorebirds in winter, as well as small shorebirds in fall and Least Terns in summer have increased in SBSPRP ponds since prior to restoration activities in 2005–2007. Counts of small shorebirds in spring remain at baseline values. Eared Grebes have increased in active salt production ponds (Coyote Hills, Dumbarton, and Mowry complexes), but not in SBSPRP ponds (Alviso, Eden Landing, and Ravenswood complexes), and Bonaparte’s gulls have declined by 18%. Since limited ponds were surveyed in 2020, meaningful comparisons to previous years’ data were restricted to a subset of sites in spring and winter. Further, no fall surveys were completed in 2020. While the results presented in this report are informative, a complete understanding of contemporary waterbird trends in the project area will require resumption of surveys at all sites in fall, winter, and spring of 2021-2022.

Phalarope migration surveys in 2020 found that counts of Wilson’s phalaropes peaked at 767 phalaropes on July 21 and counts of Red-necked phalaropes peaked at 1,700 phalaropes on August 28. The peak count of Red-necked phalaropes was higher than in 2019 (1,447 phalaropes), despite visiting fewer ponds in 2020.

As the SBSPRP progresses, we recommend a precautionary approach to waterbird management and tidal marsh restoration and maintenance of enough of the ponds within the project footprint to provide a variety of salinity and water levels suitable for many different guilds. Special consideration should be given to birds that prefer medium to high salinity ponds, such as phalaropes and Eared Grebes, since restoration activities have already reduced the prevalence of these habitat conditions and the remaining high salinity habitat is managed for salt production rather than waterbird needs. Creating or maintaining islands or undisturbed levees will provide additional nesting and roosting habitat for other guilds. As the restoration advances, continued monitoring of avian use of Cargill-managed and SBSPRP ponds will be valuable in assessing progress toward the management target of maintaining baseline waterbird numbers. However, a regional perspective will be needed to tease apart drivers of waterbird use in the project area. With more than a decade of bird and water quality monitoring data available, a useful next step will be to model bird habitat use and to use the model to predict the impact of future restoration scenarios on bird abundance.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Habitat Use by Breeding Waterbirds in Relation to Tidal Marsh Restoration in the San Francisco Bay Estuary

ariela — Tue, 27 Jun 2023 18:27:53 +0000

Habitat Use by Breeding Waterbirds in Relation to Tidal Marsh Restoration in the San Francisco Bay Estuary

Map of 2019 avocet observations

ariela Tue, 06/27/2023 - 11:27

Document Category

Scientific Reports

Author(s)

Date

2023-06

Summary

Abstract

The South Bay Salt Pond Restoration Project aims to restore many former salt production ponds, now managed for wildlife and water quality, to tidal marsh. However, because managed ponds support large densities of breeding waterbirds, reduction of pond habitat may influence breeding waterbird distribution and abundance. We investigated habitat use associated with breeding, feeding, and roosting behaviors during the breeding season for American Avocets (Recurvirostra americana), Black-necked Stilts (Himantopus mexicanus), Forster’s Terns (Sterna forsteri), and Caspian Terns (Hydroprogne caspia) in south San Francisco Bay in 2019 after substantial tidal marsh restoration, and compared results to a 2001 survey (before restoration). In 2019, managed ponds (26% of currently available habitat) were selected by waterbirds engaged in breeding behaviors (> 39% of observations), foraging (> 42%), and roosting (> 73%). Waterbirds avoided tidal habitats (43% of available habitat), comprising < 17% of observations of breeding behavior, < 28% of foraging observations, and < 13% of roosting observations. Waterbird densities increased in managed ponds between 2001 and 2019, and decreased in active salt ponds, especially among feeding Avocets (92% decrease) and Stilts (100% decrease). Islands were important for waterbirds observed breeding and roosting (45% of Avocet and 53% of Tern observations). Avocets and Stilts fed primarily on wet bare ground (65% and 58%, respectively), whereas feeding Forster’s Terns and Caspian Terns used mostly open water (82% and 93%, respectively). Within ponds, Avocets were associated with islands (131 m closer than expected). Stilts and Forster’s Terns were also associated with islands (68 m and 161 m closer than expected), except when feeding (1 m closer and 90 m farther than expected). Avocets and Stilts were associated with pond levees (39 m and 41 m closer than expected), but Forster’s Terns were not (9 m closer than expected). Our results emphasize the importance of managed ponds for breeding and foraging waterbirds, including islands for breeding and roosting and levees for foraging.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Content available here

eScholarship link to paper

Community Science-Based Colonial Waterbird Monitoring: 2016 Nesting Summary

Dave Halsing — Tue, 26 Apr 2022 18:27:33 +0000

Community Science-Based Colonial Waterbird Monitoring: 2016 Nesting Summary Dave Halsing Tue, 04/26/2022 - 11:27

Document Category

Scientific Reports

Author(s)

Max Tarjan

Kristin Butler

SFBBO

Date

2016-12

Summary

This report conveys the results of the 2016 nesting waterbird monitoring program, led by the San Francisco Bay Bird Observatory.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Community Science-Based Colonial Waterbird Monitoring: 2017 Nesting Summary

Dave Halsing — Tue, 26 Apr 2022 18:25:11 +0000

Community Science-Based Colonial Waterbird Monitoring: 2017 Nesting Summary Dave Halsing Tue, 04/26/2022 - 11:25

Document Category

Scientific Reports

Author(s)

Max Tarjan

Kristin Butler

SFBBO

Date

2017-12

Summary

This report conveys the results of the 2017 nesting waterbird monitoring program, led by the San Francisco Bay Bird Observatory.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Community Science-Based Colonial Waterbird Monitoring 2018 Nesting Summary

Dave Halsing — Tue, 26 Apr 2022 18:21:19 +0000

Community Science-Based Colonial Waterbird Monitoring 2018 Nesting Summary Dave Halsing Tue, 04/26/2022 - 11:21

Document Category

Scientific Reports

Author(s)

Max Tarjan

Kristin Butler

SFBBO

Date

2019-01

Summary

This report conveys the results of the 2018 nesting waterbird monitoring program, led by the San Francisco Bay Bird Observatory.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Community Science-Based Colonial Waterbird Monitoring: 2019 Nesting Summary

Dave Halsing — Tue, 26 Apr 2022 18:16:59 +0000

Community Science-Based Colonial Waterbird Monitoring: 2019 Nesting Summary Dave Halsing Tue, 04/26/2022 - 11:16

Document Category

Scientific Reports

Author(s)

Max Tarjan

Gabbie Burns

SFBBO

Date

2020-01

Summary

This report conveys the results of the 2019 nesting waterbird monitoring program, led by the San Francisco Bay Bird Observatory.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Community Science-Based Colonial Waterbird Monitoring: 2020 Nesting Summary

Dave Halsing — Tue, 26 Apr 2022 18:13:58 +0000

Community Science-Based Colonial Waterbird Monitoring: 2020 Nesting Summary Dave Halsing Tue, 04/26/2022 - 11:13

Document Category

Scientific Reports

Author(s)

Max Tarjan

Gabbie Burns

SFBBO

Date

2021-03

Summary

This report conveys the results of the 2020 nesting waterbird monitoring program, led by the San Francisco Bay Bird Observatory.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Coordinated phalarope surveys at western North American staging sites, 2019-2020

ariela — Sat, 16 Oct 2021 23:30:45 +0000

Coordinated phalarope surveys at western North American staging sites, 2019-2020 ariela Sat, 10/16/2021 - 16:30

Document Category

Scientific Reports

Author(s)

Date

2021-03

Summary

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