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

Alviso

Eden Landing

Ravenswood

Merging tidal datums and Lidar elevation for species distribution modeling in South San Francisco Bay

admin — Thu, 23 Nov 2017 00:21:53 +0000

Merging tidal datums and Lidar elevation for species distribution modeling in South San Francisco Bay admin Wed, 11/22/2017 - 16:21

Document Category

Scientific Reports

Author(s)

Gavin Archbald

Date

2010-12-01

Summary

Because high tides increase in elevation across South San Francisco Bay, and because tidal inundation structures tidal salt marshes plant zonation, species distribution models (SDMs) of salt marsh plants require integrated, spatially continuous measures of tidal patterns and elevation. Continuous Lidar elevation data is available for South San Francisco Bay, but tidal datum values from National Ocean Service (NOS) tidal stations in the region are available only as point locations. In order to effectively normalize Lidar elevations to tidal heights, an interpolated data layer of tidal datums was created in ArcGIS. MHHW from 16 tide stations were extracted from tidesandcurrents.noaa.gov, translated to NAVD88 using a conversion table created by NOS for a 2005 hydrographic survey, then interpolated using the spline tool in ArcGIS. Then, the lidar elevation layer was subtracted from the MHHW layer, normalizing elevation relative to MHHW and creating an input meaningful for region wide marsh vegetation distribution models. Results and sources of error in the output are discussed.

Keywords

tidal marshes

data