Habitats: Tidal Marsh

Julian Wood and Nadav Nur (PRBO Conservation Science)

Status: Tidal marsh birds are stable to increasing

Tidal marshes are the vegetated, tidally influenced wetlands found along the edges of San Francisco Bay and associated channels. Pacific cordgrass, pickleweed, and other specialized plants adapted to salty water provide important habitat for many animal species, such as young salmon and other fishes, rails, songbirds, shorebirds, egrets, ducks, and the endangered salt marsh harvest mouse. Some animals, like the indicator species here and the endangered salt marsh harvest mouse, are endemic to the tidal marshes of San Francisco Bay—meaning they do not occur anywhere else in the world. While 80% of historic tidal marsh habitat has been lost since the mid-1800s, growing marsh restoration efforts are reversing this trend and causing the acreage to increase again.

Song Sparrow – The most common tidal marsh bird is overall stable, but the last 10 years show declines.

Salt Marsh Common Yellowthroat – Prefers channels and brackish marshes and has increased since the 1990s.

California Black Rail – Recent increases give hope for this State-listed species.

Salt Marsh Common Yellowthroat

Salt Marsh Common Yellowthroat

Song Sparrow

Song Sparrow

The three species chosen to indicate the state of the tidal marsh are Song Sparrow, Common Yellowthroat, and Black Rail. Data were collected from over 200 locations throughout San Francisco Bay Estuary using 5-minute point count surveys during April–May to assess breeding season density (birds per hectare).

Song Sparrow – Stable overall (decreasing North Bay and Suisun Bay; increasing South Bay).

Salt Marsh Common Yellowthroat – Slightly increasing.

California Black Rail – Recently increasing.

Note: For California Clapper Rail, see Endangered Species section

California Black Rail

California Black Rail

Threats

Primary threat: Rising sea level resulting in some marshes "drowning" or disappearing and other marshes transitioning from fresh water to brackish marsh or from high marsh to low marsh. Limited space remains along the Bay's shoreline for marshes to expand or regenerate.

Loss and conversion of restorable marsh due to urbanization (especially in south and central Bay) threaten potential future marsh locations.

Extreme storm events push water beyond typical high tide levels, eroding marsh habitat and flooding high marsh – critical as refugia for marsh birds. High water can flood nests and push rails and other marsh animals to higher ground and adjacent urbanized areas, where they are vulnerable to predators. High water events are predicted to become more severe and more frequent with climate change.

Invasive plants, particularly invasive Spartina hybrids (crosses between native cordgrass and introduced cordgrasses), cover mudflat areas and channels, eliminating important feeding sites for shorebirds and marsh birds. Pepperweed invades marshes and channel edges, outcompeting gumplant and other native marsh plants required by Song Sparrows and Common Yellowthroats for nesting and cover.

Introduced and increased predators such as non-native red foxes, Norway rats, and house cats, and native raccoons, corvids, and gulls prey upon birds nesting in marshes surrounding the Bay. Predator numbers are usually inflated near urban areas.

Pollution, contaminants, and toxic events such as oil spills directly kill birds as well as vegetation, fish, and invertebrates. Mercury, PCBs, and other contaminants affect reproduction.

Actions

Planning, Management, and Restoration

Support and use sea level rise modeling tools to better understand impacts on tidal marsh habitat due to climate change, and to prioritize areas for preservation and restoration of marsh habitat. For an example of a model focused on predicting Bay-wide changes to the tidal marsh ecosystem, visit www.prbo.org/sfbayslr.

Identify and protect upland areas for marshes to move to as sea level rises.

Promote restoration in high-priority areas like the Petaluma and Napa River systems and South San Francisco Bay that are better able to cope with rising sea levels.

Promote re-use of clean sediment from dredged navigation channels to jump-start marsh restoration in subsided areas or to help marshes keep pace with sea level rise in the future.

Restore high-ground refugia, such as broad levee slopes and gradual upland transitions, with native vegetation to offer birds and small mammals refuge from high tide events.

Support the South Bay Salt Pond Restoration Project, and promote it as a model for future restoration efforts. This large restoration project can serve as a demonstration project, as it is being adaptively managed to ensure the most benefit to the San Francisco Bay ecosystem.

Halt development on existing or potential future baylands including salt ponds, diked baylands, and uplands with future marsh potential.

Control introduced predators such as red foxes and feral house cats, especially in areas with high concentrations of marsh birds. Educate the public about the impact of cats on bird populations, and remove feral cat feeding stations.

Reduce native predator populations (raccoon, skunk, crow, and raven) by eliminating or securing food waste in parks, residential areas, businesses, and other sources near the Bay.

Monitor and control introduced invasive plants early, when costs are lower, or when a direct threat to marsh birds is likely.

Scientists

Monitor marsh bird population sizes and reproduction annually to determine Bay-wide trends and to evaluate the success of conservation efforts. Make results known to conservation practitioners and the public.

Advance predictive modeling of future habitat conditions and bird response, to guide habitat acquisition and restoration.

Assess contaminant thresholds in birds, to evaluate impacts of mercury and other toxins to marsh birds.