Tidal Marsh
Tidal marshes are coastal wetlands that flood and drain with the tides, creating complex networks of channels, ponds, and plant zones defined by water movement and elevation. Tidal marshes support diverse wildlife communities and help keep our Bay waters clean.
The tidal marsh indicator is doing well and increasing overall. The SF Bay community is doing a good job stewarding this habitat with many important features intact.
Multi-species indicator results
The overall trend in the multi-species bird indicator for the San Francisco Bay Estuary was positive, suggesting that tidal marsh habitats continue to support a diverse assemblage of tidal marsh dependent bird species.
Indicator Species
We use birds to tell us how the habitat is doing because they’re great indicators! All subspecies in the SF Bay are year-round residents and each have unique adaptations to tidal marsh habitat occupying a slightly different niche within the ecosystem for foraging, shelter, and reproduction. Together, these bird species are excellent indicators of tidal marsh habitat quality.
Song Sparrow
Common Yellowthroat
Black Rail
Song Sparrow
There are three subspecies of Song Sparrow that are endemic to San Francisco Bay marshes. The Alameda Song Sparrow (Melospiza melodia pusillula) that occurs in the South Bay, The San Pablo Song Sparrow (M. m. samuelis), and the Suisun Song Sparrow (M. m. maxillaris) which occurs in Suisun Marsh and into the northeast Delta. All three subspecies are associated with specific habitat features within brackish and salt marshes including:
- Dense native vegetation, especially tall Salicornia (pickleweed), Grindelia (gumplant), that provide nesting cover and foraging habitat.
- Tidal marsh plains with moderate to high elevation zones that flood less frequently, offering protection for nests from tidal inundation.
- Proximity to tidal channels that provide foraging opportunities and that are lined Grindelia that is used for nesting
- Low levels of edge disturbance, such as from levees, trails, or development, since song sparrows are sensitive to habitat fragmentation and increased predator presence near urbanized edges
Common Yellowthroat
In San Francisco Bay, the Saltmarsh Common Yellowthroat (Geothlypis trichas sinuosa) is a Bird Species of Special Concern and a year-round resident that relies on specific habitat features within tidal marshes and adjacent wetland ecotones in the North and South Bay and likely Suisun Marsh. Common Yellowthroat subspecies range boundaries are not well understood and individuals in the Delta may be a different subspecies. Key characteristics that support Common Yellowthroat populations include:
- Tall, dense vegetation Typha (cattails), tule (Schoenoplectus) and Bolboschoenus (bulrushes), especially near the upland edge or in transition zones between marsh and terrestrial habitats where taller vegetation often occurs. This structure provides crucial cover for nesting and foraging.
- In addition to tidal salt marshes, they can also inhabit brackish wetlands and muted tidal marshes.
Black Rail
The California Black Rail (Laterallus jamaicensis coturniculus) is a state-threatened species that depends on marsh and other wetland habitats and is associated with key characteristics including:
- High-elevation marsh zones that are infrequently flooded, especially those dominated by dense, persistent vegetation such as alkali bulrush (Bolboschoenus maritimus).
- Dense ground-level vegetation, especially with dense structure within 30 cm of the ground, which provides concealment for this secretive rail and protection from predators.
- Small channels and shallow water features nearby, which support foraging opportunities while maintaining nearby escape cover.
- Large, contiguous marsh patches with minimal disturbance, as the species is highly sensitive to habitat fragmentation, human activity, and edge effects.
Trends by Species
Song Sparrow
[ ASPECT RATIO 12/7 ]
Trends in abundance for three endemic subspecies of Song Sparrow (Melospiza melodia, pusillula, M. m. samuelis, and M. m. maxillaris) are generally stable or increasing in the North and South Bay, with significant mid-term gains indicating relatively healthy and possibly improving marsh conditions. However, the recent sharp and statistically significant decline of this species in the Delta raises concern and may reflect local habitat stressors.
Common Yellowthroat
Common Yellowthroat (Geothlypis trichas) In the North and South Bay, the Saltmarsh Common Yellowthroat (Geothlypis trichas sinuosa) is a year-round resident exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions. Yet, the recent significant decline in Suisun signals a potential reversal in habitat quality there, which may be driven by changing hydrology or marsh structure. While other regions remain relatively stable, Suisun’s recent downturn is large enough to influence the Baywide trend, suggesting this area warrants additional attention.
[ ASPECT RATIO 4/3 ]
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions. Yet, the recent significant decline in Suisun signals a potential reversal in habitat quality there, which may be driven by changing hydrology or marsh structure. While other regions remain relatively stable, Suisun’s recent downturn is large enough to influence the Baywide trend, suggestion this area warrants additional attention.
Delta
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
Suisun
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
North
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
South
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
California Black Rail
California Black Rail (Laterallus jamaicensis coturniculus), a State of California Threatened Species that is particularly sensitive to inundation patterns and vegetation density, shows positive long-term trends in the Delta and Suisun. However, a recent significant decline in the North Bay may indicate local degradation.
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San Pablo Bay
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
Central SF Bay
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
South SF Bay
Saltmarsh Common Yellowthroats (Geothlypis thichas sinuosa) exhibit strong long-term growth in the North Bay and Suisun, pointing to historically improving conditions.
Ridgway’s Rail
The California Ridgway’s Rail (Rallus longirostris obsoletus) is a federally endangered subspecies that currently only exists in tidal marshes of San Francisco Bay from the South Bay to the North Bay.
Ridgway’s Rail abundance declined across all subregions during the 7-year period from 2018 to 2024, corresponding to an average annual decrease of 9.3% baywide (Figure 11; Table 4). However, this overall trend is primarily influenced by relatively high abundance estimates in 2018 and lower estimates in 2024, particularly in the Central and South San Francisco Bay subregions.