Tidal Marsh – Breeding Birds
What is Tidal Marsh?
Updated: 20250808
Tidal Marshes are coastal ecosystems that are influenced by the rise and fall of tides. These marshes are typically vegetated by grasses and other plants adapted to salty or brackish water. They are incredibly productive ecosystems, providing vital habitat for a wide array of wildlife, including fish, birds, and various invertebrates.
The tidal marsh multi-species bird indicator is increasing overall, suggesting that tidal marsh restoration and stewardship is working and they continue to support a diverse assemblage of tidal marsh-dependent bird species.
Tidal Marsh Multi-Species Indicator Results
Across San Francisco Bay, the multi-species bird indicator for tidal marshes shows a positive trend, indicating this habitat still supports a rich variety of bird species. This increase in bird abundance is partly due to improved and restored marsh conditions.
However, weather, like rainfall and drought, has also affected breeding success, leading to periods of both growth and decline. Notably, the three indicator species: Song Sparrows, Common Yellowthroats, and Black Rails, have increased in the North Bay and Suisun areas while South Bay populations have remained stable, even with more limited tidal marsh habitat, thanks to ongoing restoration efforts.
Tidal Marsh 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. The Ridgway’s Rail is another key indicator of marsh health and is treated separately (see below).
Song Sparrow
Common Yellowthroat
Black Rail
Methods
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.
Tidal marsh breeding bird point count surveys
Data for Song Sparrow, Common Yellowthroat, and Black Rail were collected using a 5-minute passive point count method conducted twice each year from late March through May.
Across San Francisco Bay, the multi-species bird indicator for tidal marshes shows a positive trend, indicating this habitat still supports a rich variety of bird species. This increase in bird abundance is partly due to improved and restored marsh conditions.
However, weather, like rainfall and drought, has also affected breeding success, leading to periods of both growth and decline. Notably, the three indicator species: Song Sparrows, Common Yellowthroats, and Black Rails, have increased in the North Bay and Suisun areas while South Bay populations have remained stable, even with more limited tidal marsh habitat, thanks to ongoing restoration efforts.
Trends by Species
Song Sparrow
Common Yellowthroat
California Black Rail
Ridgway’s Rail
Tidal Marsh Ridgway’s Rail Indicator Status
The Ridgway’s Rail population remains critically low and a recent short-term decline is cause for concern.
Response to tidal restoration is positive and remains one of the best strategies for recovering the population of this endangered species.
Status: Decreasing
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.
Methods
Ridgway’s Rail North American secretive marsh bird surveys
Data were collected using the USFWS Secretive Marsh Bird Protocol for SF Bay consisting of a 10-minute point count in which Ridgway’s Rail and Black Rail calls are broadcast during each survey to elicit a response. Surveys are conducted baywide three times each year during Jan-Mar in tidal marsh habitat throughout SF Bay from the South Bay to Suisun Bay.
In the short term, the number of Ridgway’s Rails has decreased across all areas. However, these numbers can greatly fluctuate, so this short term trend of decline might not last. More predators, like ravens and free-ranging domesticated cats, which have been increasing, can have significant impacts on the rail population.
Similar to other tidal marsh birds, weather patterns like extreme storm events can have significant impacts on the rail population. Restoring tidal marshes has been successful in creating high quality habitats, which helps increase the rail population.
While surveys began in 2005, the early survey methods were different, making direct comparisons to current surveys difficult. However, previous studies indicate the population dropped between 2005 and 2009 and has remained at lower levels ever since.
Seasonal pond
Brief note about hydrology, amphibians, and shorebird use.
Common Yellowthroat
Shrub and tall-grass breeder. Indicator of dense emergent cover.
Ridgway's Rail
Tidal marsh specialist. Needs continuous cover and channel edges.
Gumplant (Grindelia)
Nectar and structure for insects and birds. Restoration value.
Great Egret
Feeds along channels. Sensitive to disturbance and turbidity.
Dowitcher
Uses shallow muddy margins for probing. Migration stopover.