Science for a Blue Planet

Featuring cutting-edge work, discoveries, and challenges of our scientists, our partners, and the larger conservation science community.

Re-imagining Ridgway’s Rails

The complexity and creativity of recovering a species in San Francisco Bay

It’s complicated. That may only begin to describe recovering the endangered California Ridgway’s Rail and the San Francisco Bay habitat it needs to survive.

This chicken-sized, secretive bird is flummoxing—not only in what to call it but also in how it can possibly thrive within its specific marsh ecosystem, where daily tides send it seeking higher ground at the mercy of falcons and other predators.

Just last year, ornithologists changed the bird’s name from the California Clapper Rail to the Ridgway’s Rail, due to new genetic research. It turns out the bird, which rarely flies and sometimes squawks loudly but can be difficult for trained biologists to find, is not related to the Clapper Rails on the East Coast.

Meanwhile, Ridgway’s Rail numbers, hovering near 1,000 individuals, are now about the same as when the U.S. Fish and Wildlife Service listed the bird as endangered in 1970. Since then, the bird’s story contains twists and turns, like a surprising population drop in the mid-2000s, unexpected results from man-made floating islands, more habitat loss predicted with sea-level rise and, at last, some hope with large tidal marsh restorations currently underway.

Ridgway's Rail in native habitat. Photo: Tom Grey
Ridgway’s Rail in native habitat. Photo: Tom Grey

“This is a challenging one,” says Cory Overton, wildlife biologist with the U.S. Geological Survey’s Western Ecology Center in Davis, Calif. “We’re talking about a history that began 150 years ago with changes in land use. Now, over seven million people live in the Bay Area, and we’re trying to restore habitat that takes decades to create for a species that sometimes only lives nine months.”

Even before losing over 80 percent of their historical habitat to in-filling and development, the Rails occupied a narrow slice of habitat, the inter-tidal zone or salt marsh mudflats where they scavenge for crabs, mussels, clams, snails and small fish. The birds seek higher ground and cover when the tides come in and, yet, it’s not unusual for them to stay within the same marsh during their entire lifetime.

The Rails now primarily inhabit USFWS national wildlife refuges and state and local natural areas in San Pablo Bay and in south San Francisco Bay. Endangered Species Act regulations can make it challenging to get the permissions to study the birds—and even more difficult to restore tidal marsh habitat in innovative ways. In addition, funding for bird studies has dropped off in recent years after federal budget cuts.

Still, Overton and a group of area scientists from local, state and national conservation agencies and nonprofits are working to study the Ridgway’s Rail and restore its habitat. They’ve learned a few lessons along the way.

When Opposites Attract

The takeover began slowly in the 1990s. But, within a decade, invasive Spartina consumed large swaths of south San Francisco Bay tidal marsh habitat. (San Pablo Bay remains largely free of invasive Spartina.)

Surprisingly, the invasive plant is a hybrid of the native Spartina foliosa, also called Pacific cordgrass, and Spartina alterniflora, or smooth cordgrass, introduced from the East Coast. The native cordgrass and other native marsh plants provide healthy habitat for Rails and the dozens other wildlife species using the marshes. Unfortunately, invasive Spartina grows into a taller, denser mono-culture than the area’s native plants.

Invasive Spartina.
Invasive Spartina.

Since invasive Spartina threatens to take over tidal marshes to the detriment of other native shorebirds and songbirds, the California Coastal Conservancy launched the Invasive Spartina Project in 2003. This collaboration among local, state and federal agencies and groups, such as the USFWS, began a large-scale invasive Spartina eradication effort using herbicide and manual removal. The effort successfully removed a large percentage of the invasive plants over the next dozen years. However, the Rails had moved into invaded areas and their numbers in the south Bay fell by almost half during that time.

This was after the Bay-wide population recovered from less than a 1,000 individuals in the early 1990s to a peak of a few thousand in 2007.

“The Rail population trends mirror the hybrid Spartina invasion in the south Bay,” Overton says. “Overall, they increased along with the invasion and declined following efforts to eradicate hybrid Spartina.”

Overton and colleagues monitored the survival rates of 108 radio-marked Rails from 2007 to 2010. Most of the Rails they monitored died during that time period due to predation from raptors or mammals. Before eradication, the hybrid Spartina provided the cover the Rails needed during high tide to protect themselves from predators like Short-eared Owl, Peregrine Falcon, Kestrel, red fox and feral cats.

A higher percentage of predation occurred during the winter, when restored or existing native vegetation died back and storm surges were larger. Overton says the native vegetation may have better protected the Rails historically, when there were large marshes with a range of elevations. In addition, predators are more voracious now, squeezed into smaller and highly fragmented areas.

“Recovering Rails may take different strategies in different areas,” he says. “An invasive plant is not the best option but maybe our preferred alternative has to be delayed and we can use invasive Spartina to speed up recovery in places.”

Julian Wood, San Francisco Bay program manager for Point Blue Conservation Science, agrees recovery is going to take creativity, especially when considering the multiple species using the tidal marshes but says allowing invasive Spartina to persist is a risky strategy.

“We can’t focus on single-species recovery,” Wood says. “Invasive Spartina might help Rails in the short term in some areas but it will harm other species. Sometimes we have to make short-term sacrifices to restore the most fully functioning ecosystem we can.  The fact that Rails in San Pablo Bay, which has been spared from the invasion, are rebounding faster from the population crash gives me hope that diverse, native marshes still hold the answer.”

Island Life

It turns out Ridgway’s Rails don’t mind being afloat. During the winter of 2010, a partnership of USGS, USFWS and the Coastal Conservancy started placing artificial floating islands with vegetative cover in Arrowhead Marsh near Oakland. The results were overwhelmingly positive.

The scientists tethered the islands, about the size of a twin bed and made up of recycled plastic and high-density foam, using anchors and nylon rope that was long enough to ensure they floated during the highest tides. Each island was covered in woven-palm screens over a meter tall to provide Rails cover from predators.

Floating islands (here in the south Bay) can provide Rails cover during high tides. Photo: USGS
Floating islands can provide Rails cover during high tides. Photo: USGS

Using motion-detection cameras, Overton and his team recorded Rails using the islands over 85,000 times during that first winter. Over the next few years, the team found that the birds were 300 times more likely to use the islands than the surrounding habitat during high tides and in daylight hours, when predators are more prevalent in the area.

“It may be that we have to actively manage this species in perpetuity with options like floating islands,” Overton says. “How else does a species live when its habitat continually changes? The San Francisco Bay is a highly invaded ecosystem and more changes are expected with rising sea levels.”

Indeed, San Francisco Bay sea-level rise predictions for this century hover from 40 to over 160 centimeters. This could mean that over 90 percent of existing tidal marsh habitat could be washed away, or converted to mudflats, by 2100. The marshes that do remain will be flooded more often by an increasing number of large storms.

Losing more of this tidal refuge habitat will prove difficult for Rails since they inhabit small ranges and their populations are already highly fragmented. Yet, Overton says the limited availability of habitat may be alleviated at some level by using artificial material, such as floating islands, and through intensive and innovative tidal marsh restoration.

A Game of Inches

The list of partners is long. Two projects in particular, one near Sears Point in Sonoma County and one near Mare Island in Solano County, are bringing together a host of local, state and national agencies and organizations to restore tidal marsh habitat on over 2,500 acres in the north Bay. This is in addition to other projects, including the South Bay Salt Pond Restoration near San Jose, a scattered group of parcels totaling over 15,000 acres and, together, considered the largest tidal marsh restoration on the West Coast.

A Point Blue scientist crosses tidal marsh while monitoring Rail numbers in north San Francisco Bay. Photo: Point Blue
A Point Blue scientist crosses tidal marsh while monitoring Rail numbers in San Pablo Bay. Photo: Point Blue

These multi-phase restoration projects include a mix of levee breaches, sediment infilling to increase marsh levels, native plantings, and creating mounds within the marsh to provide refuge from high tides. The work will take decades to accomplish and is expected to also provide recreation opportunities and flood control, and help improve water quality.

The balanced management of invasive Spartina, use of artificial habitat and larger restoration projects may over time provide a network of habitat corridors for Rails, and other wildlife, and help the Rail population recover.

“It’s a game of inches and of patience. After restoration on the South Bay Salt Ponds, it still took five years before one Rail showed up,” Overton says. “But there is room for optimism. We’re not going to have 5,000-acre intact marshlands, but we might be able to re-create conditions that are more sustainable.”

After all this work, waiting to see if these squawking, “marsh hens” appear—and then find places to hide from predators during high tides—may be the hardest part.

“Restoring tidal marshes doesn’t happen overnight,” Wood says. “But we have examples of Rails returning to breed in sites that were dry fields just 15 years earlier. The massive scale of tidal marsh restoration happening now gives me hope that in my lifetime I will witness a thriving Rail population in San Francisco Bay.”

Overton concurs with this positive outlook.

“I have the greatest hope in the intelligent and highly motivated people of the Bay Area who value their natural areas and want to be a part of the solution,” he says. “This situation was 150 years in the making, but I believe Rails are tenacious and they will hold on. I believe they will survive as long as they have places where they can go.”


Main photo: Tom Grey

Learn more about Point Blue’s work in San Francisco Bay here.

Opinions expressed in Science for a Blue Planet posts do not necessarily reflect the views of Point Blue Conservation Science or the many partners involved in restoring San Francisco Bay habitat.