Katie LaBarbera

Western Snowy Plover and California Least Tern Monitoring in the San Francisco Bay Annual Report 2023

ariela — Sat, 27 Jan 2024 00:03:59 +0000

Western Snowy Plover and California Least Tern Monitoring in the San Francisco Bay Annual Report 2023

Three snowy plover chicks

ariela Fri, 01/26/2024 - 16:03

Document Category

Scientific Reports

Author(s)

Date

2024-01

Summary

Excerpts from Executive Summary

During the 2023 breeding season, SFBBO monitored Snowy Plover population size, nesting and fledging success, the use of experimental habitat enhancement sites, and potential predators at eight historical salt production pond complexes in the South San Francisco Bay.

During the Pacific Coast rangewide winter window survey (January 26 – 30, 2023) SFBBO and other organizations counted a total of 262 adult Snowy Plovers within RU3, while during the breeding season window survey (May 20 – 27, 2023), SFBBO and other organizations counted a total of 368 adult Snowy Plovers within RU3. Over the course of the breeding season (March – September), SFBBO staff determined and documented the fates of 304 Snowy Plover nests in the South San Francisco Bay. Of the 304 nests monitored by SFBBO, 64% hatched, 31% were depredated, 2% were flooded, 1% fell to miscellaneous other fates and 2% were unknown. An additional 39 nests were detected at the brood stage.

Other members of RU3 documented a total of 23 nests. Among these 23 nests, 43% hatched, 35% were depredated, 13% fell to miscellaneous other fates, and 9% were unknown. An additional eight nests were documented at the brood stage.

SFBBO banded 194 Snowy Plover chicks from nests that successfully hatched within Alviso, Dumbarton, ELER, Ravenswood, and Warm Springs nesting ponds, representing 38 percent of all chicks known to have hatched from SFBBO monitored sites in the South Bay. From band re-sighting surveys and reports from other scientists and birders across the species’ range, we determined that at least 64 of these chicks survived to fledge (fully flight capable, at least 28 days post-hatching) as of December 12, 2023, resulting in an estimated apparent fledging success of 33 percent. Due to concerns regarding highly pathogenic avian influenza (HPAI), we limited our adult banding efforts. We recaptured and re-banded three adults whose bands had been damaged. Comparing adult band re-sighting and fledged juvenile data from 2022, we found return rates of 58% (n=63) for adults banded in or before 2022 and 60% (n=62) for 2022 fledges.

During avian predator surveys, we counted California Gulls (Larus californicus) and unidentified gulls (Larus spp.; likely California Gulls due to the time of year and locations) as the most numerous potential avian predators in Snowy Plover nesting areas. Common Ravens (Corvus corax), American Crows (Corvus brachyrhynchos), Snowy Egrets (Egretta thula), and Great Egrets (Ardea alba) were the next most commonly observed predator species. Two avian species and one mammalian species were confirmed as predators of Snowy Plovers in 2023 due to the following observations: a Northern Harrier depredating an incubating female Snowy Plover at A12, as reported by HT Harvey and Associates; a California Gull depredating a Snowy Plover chick at PP1; and red fox scat with Snowy Plover color bands embedded in it at E14.

We continued to monitor Snowy Plover use of oyster shell plots, which were spread in September 2014 in two areas of ELER pond E14 (Western = 6.47 ha; Eastern = 13.76 ha) as a large scale habitat enhancement project. We monitored 39 Snowy Plover nests in E14 and found an additional three nests at the brood stage; at least 24 nests were found within one of the shell plots. Chi-square analyses indicated that based upon available habitat, breeding Snowy Plovers preferred to nest in shelled plots. Nest survival analyses found the daily nest survival (DSR) to be 98.3% with a 60.9% chance that a nest would survive to hatch (33 days).

2023 marked the seventh consecutive year that California Least Terns (Sternula antillarum browni; Least Terns) nested at pond E14. This year Least Terns also nested on the levee between ponds E12 and E13, on a constructed island on E13, and for the first time on pond E6B. On March 4, 2023, we led a volunteer event to remove encroaching vegetation, spread oyster shells, and place 15 wooden chick shelters within the Western Shell Plot of E14. Least Terns were first observed at ELER on May 2, when an unknown number of adults were heard flying over E14. The maximum number of adults recorded on-site was 55 on July 11. A total of 77 nests were monitored between ponds E6B, E12, E13, and E14. In E14, a total of 22 nests were monitored, with two confirmed to have hatched. Eighteen failed (did not hatch due to depredation, abandonment, or flooded out), and the fate of two nests could not be determined. No fledglings were produced from E14. At E12 and E13, a total of 25 nests were monitored, with three confirmed to have hatched and three more presumed to have hatched. Sixteen nests failed and the fate of three nests could not be determined. Between three and four fledglings are estimated to have been produced from E13. At E6B, a total of 30 nests were monitored, with seven confirmed to have hatched and an additional eight presumed to have hatched. The other 15 nests failed. Based on scat and prints, SFBBO suspects that red foxes depredated the majority of the Least Tern nests in ELER.

In 2023, SFBBO continued to interface with the various land and project managers throughout the South Bay, including the South Bay Salt Pond Restoration Project (SBSPRP), whose actions are reshaping the Bay’s ecosystems and seriously impacting Snowy Plovers and Least Terns. During Phase 1 of the SBSPRP, restoration and reconfiguration of ponds that formerly supported Snowy Plover breeding habitat resulted in the loss of roughly 19% of available breeding habitat for Snowy Plovers. To account for the decline in available habitat, new water control structures were installed in many ponds at Don Edwards SFBNWR and ELER to allow for better management of habitat. In 2022 and 2023 respectively, we recorded the second highest (288) and highest (368) breeding population sizes ever recorded in RU3, suggesting a growing population size. However, since 2020, the proportion of breeding adult Snowy Plovers found on SBSPRP lands compared to all of RU3 has consistently been under 80 percent, when the lowest it had previously dropped between 2003 and 2019 was 83 percent in 2018. Some of this lower ratio can be attributed to expanded survey efforts across RU3, but the recent movement of Snowy Plovers away from high density nesting at E14, and instead diversifying to sites across RU3 is also relevant. In order to reach the SBSPRP and RU3 goals of 250 and 500 breeding birds, respectively, it will likely be necessary to provide multiple enhanced breeding ponds, both locally and throughout RU3, in conjunction with targeted predator control efforts to reduce predation pressure on any one pond.

Phase 2 restoration on Refuge lands includes restoration activities at the Ravenswood Complex (R3, R4, R5/S5), Alviso Complex (A8 Ponds: A8, Mountain View Ponds: A1, A2W and the Island Ponds: A19, A20). Pond R3 has been enhanced for Snowy Plovers by adding water management capabilities with the addition of a new water control structure. However, overall Phase 2 actions at the Refuge have still resulted in an additional 8% loss of remaining available breeding habitat due to the breaching of R4 in December 2023. It will be critical to enhance remaining Snowy Plover breeding habitat at R1 through R3 and SF2 to account for the higher density of breeding that will likely occur in these areas. Reduced habitat availability could result in increased predation pressure at the Ravenswood Complex. Furthermore, increased development adjacent to these restoration sites artificially inflates human commensal predator populations such as skunks, feral cats, American Crows, and Common Ravens by supplementing food and complicating predator management opportunities in locations with high visitor use. Without additional enhancement and informed predator control efforts, population growth at one of the most important breeding sites in RU3 could be impeded.

Currently, most breeding plovers in RU3 are found in the South Bay, and a large proportion of those plovers breed on SBSPRP lands. We recommend that the SBSPRP plan Phase 2 construction activities to avoid negatively impacting breeding Snowy Plovers, as was done in Phase 1. This includes providing alternative breeding habitats when construction activities impact or eliminate Snowy Plover nesting ponds and scheduling construction activities before or after the Snowy Plover breeding season when possible.

The recovery of the RU3 plover population depends on the continued availability of suitable habitats, which are currently owned and managed by multiple landowners. Providing quality habitat at spatially diverse locations throughout RU3 is a critical strategy to prevent population decline caused by overconcentration of breeding in any one area. Our research over the past nine years at E14 highlights that “placing all the eggs in one basket” is not an effective long-term strategy for meeting recovery goals. Adaptive management strategies on SBSPRP land to balance tidal restoration with Snowy Plover needs, despite the increased cost of managing ponds and future concerns about sea level rise adaptation, could serve as a positive example for other landowners. Aside from the SBSPRP, other RU3 landowners have not adequately accounted for Snowy Plovers when making land management and restoration decisions, particularly in the North Bay where Snowy Plovers were long known to breed in former salt production ponds but have been left with minimal nesting habitat following widespread tidal marsh restoration. Management actions by the SBSPRP to balance tidal marsh and pond dependent species should be continued in future seasons, including management of multiple ponds with a mixture of exposed pond and shallow water depth during the winter and the implementation of large scale shell, gravel, and/or cobble enhancement to attract Snowy Plovers to appropriate nesting ponds.

Thus we recommend that Refuge biologists and USFWS Snowy Plover Recovery Leads continue to promote enhancement, management, and maintenance of Snowy Plover habitat on SBSPRP land, and encourage the Bay Delta Fish and Wildlife Office and landowners to increase efforts to identify suitable habitat in the rest of RU3 that can be enhanced or managed for breeding Snowy Plovers and maintain existing Snowy Plover habitat when feasible as outlined in the Recovery Plan (USFWS 2007). In addition, we recommend that all managers communicate and coordinate tidal marsh restoration activities to ensure that adequate Snowy Plover breeding habitat will remain to support recovery throughout RU3.

Keywords

Phalarope Migration Surveys June – September 2022

ariela — Wed, 31 May 2023 20:02:28 +0000

Phalarope Migration Surveys June – September 2022 ariela Wed, 05/31/2023 - 13:02

Document Category

Scientific Reports

Author(s)

Date

2023-04

Summary

EXECUTIVE SUMMARY
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. These wetlands provide habitat
for many waterbirds, including migrating red-necked phalarope (Phalaropus lobatus) and Wilson’s
phalarope (P. tricolor). Sustaining baseline population goals for wildlife populations requires
understanding how species are responding to restoration actions over time. While many waterbird guilds
have increased in abundance from pre-restoration baselines, surveys in 2017 showed phalarope numbers
declined by 78% compared to pre-restoration baseline monthly summer average of 3225 birds has
warranted ongoing phalarope studies. The purpose of this ongoing study is to understand observed
declines in phalarope numbers within the SBSPRP area and their relationship with broader population
trends and phalarope movements. This report serves as a data summary and coarse-scale assessment of
phalarope monitoring efforts in the South San Francisco Bay during the 2022 migration.

From June 21, 2022 to September 27, 2022, we conducted phalarope migration surveys at 31 sites (17
SBSPRP-managed former salt ponds, 7 Cargill-managed salt production ponds, and 7 additional non-salt
pond sites). The surveys found that counts of Wilson’s phalaropes peaked at 735 phalaropes on 07/19/22
and counts of red-necked phalaropes peaked at 4357 phalaropes on 08/30/22. Across all sites, a total of
13039 phalaropes were counted throughout the summer (1100 Wilson’s, 11032 red-necked, and 907 that
could not be identified to species). Looking only at the 24 current and former salt pond sites within the
study area, a total of 8698 phalaropes were counted throughout the survey season (2 Wilson’s, 7896
red-necked, and 755 that could not be identified to species). The total and peak counts for Wilson’s
phalarope were similar to 2021 data while the total and peak counts for red-necked phalaropes were both
somewhat lower. The proportion of unidentified phalaropes relative to total observations decreased
slightly from 2021 and continues to be a complicating factor in species-level analysis, but taking the
measure of assigning them to the most likely based on survey date does not change the peak counts/dates
or the direction of the trends for season totals for either species. Calculations to compare these survey data
against the NEPA/CEQA baseline show that phalarope abundance continues to be below the management
trigger of more than 50% below baseline values.

At the pond-level, phalarope abundance did not align with expectations around their preference for
high-salinity ponds. The majority of phalaropes (96%) were found in medium- and low-salinity sites,
suggesting that they may be using different selection criteria. As the SBSPRP progresses, we recommend
a precautionary approach to waterbird habitat management and tidal marsh restoration. To the extent
feasible, ponds within the project area should be maintained to provide a variety of salinity and water
levels suitable for different guilds. Given the limited number of ponds that can be maintained under sea
level rise, studies are needed to identify the specific salinity and water level characteristics that cannot be
provided by restored tidal marsh for habitat specialist species. Special consideration should be given to
understanding what influences phalarope site selection and preserving ponds with those characteristics.

Continued dedicated monitoring of phalaropes and analysis with habitat and external regional datasets
will be valuable in assessing the decline in survey counts since pre-restoration baselines. Future phalarope
migration surveys are needed to estimate inter-year changes in abundance that could be used to assess the
relative importance of broader-scale climatic drivers (or breeding ground conditions) versus local management and habitat characteristics on the observed declines. Few phalaropes were observed during
the new June survey date, but these surveys allowed us to definitively identify the peak of migration,
which was not possible in 2021 because the highest counts that year were in early July (the previous first
survey date). Future study of Motus data when it is available will aid in estimating population sizes and
understanding phalarope migration between stopover sites.

Keywords

Pond Complex

Alviso

Eden Landing

Ravenswood

Review and analysis of historical phalarope population trends

ariela — Wed, 31 May 2023 19:54:28 +0000

Review and analysis of historical phalarope population trends ariela Wed, 05/31/2023 - 12:54

Document Category

Scientific Reports

Author(s)

Date

2023-04

Summary

EXECUTIVE SUMMARY
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. These wetlands
provide habitat for many waterbirds, including migrating red-necked phalarope (Phalaropus
lobatus) and Wilson’s phalarope (P. tricolor). Sustaining baseline population goals for wildlife
populations requires understanding how species are responding to restoration actions over time.
If a species group is observed to drop below a sustained threshold or hit a single-year trigger
point below that baseline, the Project is committed to evaluating available data and considering
targeted management action. Part of this consideration is whether the decline is likely a result of
restoration actions. In 2017, phalarope counts were below their assigned trigger point. Now we
seek to understand how this observed decline in the salt ponds compares to broader population
trends throughout the phalaropes’ Western migration routes.

We reviewed a combination of existing scientific survey data and community science data to
gain insight into phalarope abundance and how it has changed over time. In July 1986,
coordinated Wilson’s phalarope surveys across migration stopover sites yielded peak counts of
741,000, including 40,000 (5% of the total count) in South San Francisco Bay. By the early
1990’s, peak Wilson’s phalarope counts at the three largest migration sites had dropped by 50%.
Range-wide data is not available for red-necked phalaropes, but it was estimated that
52,000–65,000 passed through Mono Lake each year during the early 1980’s.

The next regular scientific surveys of phalaropes at migration sites began in 2019 and are
ongoing. Counts have varied across years and no clear directional trends have emerged. The
Wilson’s phalarope peak count was highest in 2019 (370,770) and lowest in 2022 (just under
200,000). The red-necked phalarope peak count was highest in 2019 (296,731 birds) and lowest
in 2021 (124,048). In 2021, counts from SFBBO’s Phalarope Migration Surveys represented less
than 1% of the total counts during peak periods. The 2022 peak count for Wilson’s phalarope
(735 birds) represents a decline of 98% from the 1986 survey data.

The time period of greatest interest for our purposes (2005–2018) is part of the gap between
scientific surveys of phalarope numbers. To shed light on this period, we performed an analysis
of community science data submitted to the eBird platform. We used negative binomial linear
models to investigate trends in phalarope counts while controlling for survey effort at several
geographic scales, ranging from three Bay Area counties to the state of California. We found that
phalarope counts had declined steeply from the early 1970s to the late 1990s, and from then to
the present showed a continuing but more shallow decline. The three Refuge counties (Alameda,
San Mateo, and Santa Clara) had higher counts than the rest of California in the 1970s, but
declined more steeply in the following two decades. Analysis of only the most recent 20 years
(2002-2022) found no significant difference in estimated population trends between the Refuge
counties and the rest of California, although the nature of eBird data makes this a relatively
insensitive analysis.

Keywords

Pond Complex