Nature Notes: A Rainy Day in the Bay

By Rebecca Crebbin-Coates, Communications and Development Intern

If your home has a leaky roof, winter storms bring the incessant drip-drip of rain onto your living room floor.  For creatures living in a tidal marsh, big winter storms mean a lot more than a few drops of water on the carpet – they can mean an altered or flooded home.

Some organisms love heavy rain. Winter storms provide the perfect window of opportunity for many plants to germinate in intertidal marsh areas. Tidal marshes, or salt marshes, are filled with plants adapted to tolerate salt water. But even here, some plants tolerate more salt than others. For example, the invasive smooth cordgrass handles salty conditions better than Pacific cordgrass, a native species.  Heavy rains make the soil wetter and less salty. These conditions make it easier for less salt-tolerant plants like the Pacific cordgrass to thrive.

For marsh birds, storms can be dangerous. High water levels often lead to flooded nests – a significant cause of mortality. Fortunately, many marsh birds have developed specific adaptations to deal with floods from winter storms and from especially high tides throughout the year.  For example, a number of birds, like some members of the gull family, build their nests to float as the water rises, which keeps their homes safe.

Unlike the gulls, the endangered Clapper Rail attaches its nest to cordgrass stems, leaving limited possibilities for floating with storms. Adding to their innate vulnerability to flooding, Clapper Rails also love to nest in low elevations. To compensate, Clapper Rails build the ‘skyscrapers’ of the tidal marsh to protect their young. Like coastal homes that are built on stilts, Clapper Rails build brood nests in tall vegetation. Some rails may construct pillars of nesting material that keep the contents of the nest elevated anywhere from six inches to over two feet from the ground. Not high enough? Rails have been spotted increasing the height of their nests during the middle of a flood. What happens when emergency construction still isn’t enough? Clapper Rails, like many other marsh birds, will re-nest after floods as many times as necessary to ensure survival of their home.

During breeding season in the spring, additional adaptations help marsh birds keep their eggs safe from tidal flooding. Song Sparrows, native to Bay Area salt marshes, breed earlier than upland sparrows by about 15 days. This allows them to avoid having vulnerable eggs during the highest tides, which occur later in the season. Song Sparrows and Clapper Rails, along with other species, also have eggs that withstand a brief saltwater dunking without harm.

Storms and high water levels are as much a fact of life for us as they are for marsh birds and plants.  So next time you open an umbrella, jump in a puddle, or watch the tide come in, contemplate what changes water brings to your surroundings. May we appreciate the positive effects of a deluge like the plants do, and deal with its consequences with as much preparedness, patience, and perseverance as the birds have.




Noe GB, and Zedler JB.  2001.  Variable rainfall limits the germination of upper intertidal marsh plants in southern California.  Estuaries 24(1): 30-40.

Reinert SE.  2006.  Avian nesting response to tidal-marsh flooding: literature review and a case for adaptation in the red-winged blackbird.  In: Greenberg R, Maldonado JE, Droege S, and McDonald MV, Associate Eds.  Terrestrial vertebrates of tidal marshes: evolution, ecology, and conservation.  Studies in Avian Biology No. 32.  Cooper Ornithological Society.

San Francisco Bay Joint Venture.  2008.  Wetland restoration and projected impacts from climate change.  Recommendations for and by partners of the San Francisco Bay Joint Venture.  Fairfax: CA.

U.S. Environmental Protection Agency.  2010.  Endangered Species Facts: California Clapper Rail.  <>