Clapper Rail

Julian Wood, Len Liu, and Nadav Nur (PRBO Conservation Science)

Status: Decreasing

California Clapper Rails nest in the tidal marshes of the San Francisco Bay and recovery of this species has been a primary impetus for marsh restoration around the Bay. Unfortunately, the Clapper Rail struggles to survive because of habitat loss, predator pressure, and invasive species. The growing threat from sea level rise also threatens the Clapper Rail.

Clapper Rail populations have declined since the 1970s. Population estimates using different methods from published and unpublished sources should be interpreted with caution.

Standardized Bay-wide point count surveys for Clapper Rails show a steep decline that may be leveling off.

Clapper Rails in San Francisco Bay have decreased dramatically from the tens of thousands that roamed the undiked marshes before the California Gold Rush.

Hunting, then development reduced populations and pushed Clapper Rails into smaller marshes separated by urban landscapes.

More recently, the rail population hit a low point in the early 1990s, likely due to predation by non-native red foxes. The Clapper Rail's rebound during the 1990s was possibly due to fox control but also coincided with the rapid invasion of a tall non-native plant (invasive Spartina). This invader benefited rails because it provided nesting habitat and protection from predators and high tides.

Beginning in the mid-2000s, the rail population declined sharply, due in part to the removal of invasive Spartina, which threatens tidal flat and marsh ecosystems as a whole. This recent decline may be leveling off, but the future of Clapper Rails in San Francisco Bay remains tenuous. However, we can be hopeful that as thousands of acres are being restored to tidal marsh habitat, California Clapper Rails will be back on the road to recovery.

Threats

Primary threat: Predators, including introduced species such as Norway rats, house cats, and red foxes prey on Clapper Rails and their nests. Some native species of raptors, snakes, and mammals also prey on Clapper Rails.

Invasive non-native plant species can reduce nesting and foraging habitat for Clapper Rails, even changing the invertebrate community on which they feed. Perennial pepperweed reduces high-tide refugia, and hybrid Spartina may reduce channel and mudflat areas important for foraging rails. However, invasive plant control/removal decisions should always consider short-term and long- term effects on birds (e.g., invasive Spartina eradication may have contributed to significant reductions in Clapper Rail populations at some sites and should proceed with caution).

Pollution, contaminants, and toxic spills (including oil spills) directly kill rails, vegetation, fish, and the invertebrate community that sustains marsh wildlife. Toxins (e.g., mercury, lead) accumulate in rails, impairing their reproduction and survival.

Rising sea levels from global climate change will drown some marshes and increase nest flooding, making the habitat unsuitable for Clapper Rails. See www.prbo.org/sfbayslr to view maps of projected change in marsh habitat and changes in bird and plant species distribution.

Actions

Planning, Management, and Restoration

Prioritize sites: Use the most current and thorough scientific modeling of climate change scenarios to prioritize areas for acquisition and restoration (an example is PRBO’s sea level rise modeling tool: www.prbo.org/sfbayslr).

Acquire and restore uplands and diked areas where current shoreline marsh may migrate as sea level rises.

Control predators by eliminating cat feeding stations, supporting predator control programs, and keeping marshes, public parks, and adjacent housing areas free of garbage.

Enforce regulations on unlawful recreation in sensitive marshes.

Conduct active marsh planting in restored areas where plants are not regenerating on their own, or in sites where non-native plant removal has reduced overall plant cover.

Restore high ground adjacent to marshes, such as levees and uplands with dense vegetation, to offer birds refuge from high-tide events.

Locate public access points and trails to the Bay shore away from Clapper Rail habitat.

Continue funding and support for tidal marsh restoration such as the South Bay Salt Pond Restoration Project, which aims to restore over 15,100 acres of former salt ponds to a diversity of habitat types to benefit all birds, including tidal marsh-dependent species.

Scientists

Support research that seeks to understand marsh development processes in the face of sea level rise, as well as potential management actions that can mitigate these impacts.

Study the effect of trail use on Clapper Rails – both direct impacts from disturbance as well as potential increased predator access from trails.

Support research on Clapper Rail population trends (including reproductive success, which has not been closely studied at a Bay-wide scale), habitat use, and the impacts of invasive hybrid Spartina and its removal.

Support research that can inform how to create upland transition zone habitat as refugia for Clapper Rails.

Update habitat models as new data become available, to better predict areas where tidal marsh will persist given sea level rise.

Success Story • Carl's Marsh

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