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Refuge Habitats

Mudflats, seemingly barren, are actually teeming with life. A handful of Bay mud may contain 40,000 tiny living creatures! The secret of the mudflat abundance is the two tidal cycles that occur each day. Tidal water flowing in and out of the Bay creates strong currents that distribute enormous quantities of nutrients throughout the Bay, sloughs and marshes. Fish and shorebirds feast on the abundant creatures brought in by the tide, which include zooplankton such as copepods. At low tide, dowitchers, American avocets, black-necked stilts and willets can be seen probing and sweeping the mud for tasty worms, insects and shellfish.

Salt marshes are one of the most productive habitats on Earth. Food produced in salt marshes creates the foundation of many food webs. Nutrients produced in the marsh are carried out via sloughs to the plants, invertebrates and fish of the open Bay. Plants that thrive in salt marshes (such as pickleweed, cord grass, and salt grass) have adapted to the Bay's salty water. The endangered California clapper rail, the endangered salt marsh harvest mouse, and the salt marsh song sparrow all make their homes in the salt marshes.

Salt Ponds - Salt production in the Bay area involves the use of a series of salt ponds. As the water moves from one pond to the next, evaporation causes successive ponds to become saltier. Plant and animal species found in a given salt pond are determined by the concentration of salt. Fish such as topsmelt, goby, killifish and perch thrive in low to moderately salty waters.

Endangered California least terns take advantage of these fish populations, while phalaropes and black-necked stilts feed on the abundant brine shrimp of saltier ponds.

Vernal pools are short-lived, seasonal wetlands. Several species, such as endangered vernal pool tadpole shrimp and Contra Costa goldfields, are found only in this type of wetland. Resident wildlife are well adapted to the alternating wet and dry periods, with most animals and plants taking advantage of winter and spring rains to reproduce. As the pools dry in the spring, yellow goldfields and purple downingia rim the pools with brilliant color. Some animals, such as fairy shrimp and other invertebrates remain as dormant eggs throughout the long, dry summers. Adult amphibians such as the California tiger salamander leave the vernal pools during the summer months.

Upland Habitat - Rising above the salt marsh is the drier upland habitat, where jackrabbits, fence lizards, and California towhees are found. Coyote brush, oaks and a variety of grasses provide plenty of cover for these animals. Native gray foxes can find enough rodents, rabbits, insects and fruits to satisfy their hunger, while rabbits will feast upon the vegetation and grains found on the Refuge.