Don Edwards
SF Bay Home

About Us

Documents &
Brochures

Activity Schedule

Recreation

Environmental
Education

Volunteering

Jobs & Internships

Tideline Newsletter

Related Links

Directions

Black Rail, cont.

relatively rare, they present a period of high vulnerability to rails (and mice and shrews) who, for a period of several hours at a time, are refugees from their preferred habitat. The frequency of flooding has increased in recent years and, by all indication, will increase in the future. The increased height and duration of tidal inundation are caused by several factors acting in concert: rising sea level (more than one meter in the last 100 years), marsh subsidence from filling and ground water extraction, heavy rainfall associated with El Niño, and greater retention time of flood waters exacerbated by more roads, levees, and urban development along the bayshore. As the size of the bay is decreased, the volume of water has less area to inundate, so the depth becomes greater. This effect is amplified during severe storm events.

When forced out from the protective cover of pickleweed, salt grass, sedge and other marsh vegetation by rising water levels, the birds take refuge beneath whatever overhead cover they may find on the upland edge of the tideline. Historically, the transition zone was heavily vegetated with overhanging willows, coyote bush, and perennial bunchgrasses. Now the upland edge is more often a rip-rapped levee grazed to the nub, or salt ponds bound by barren dirt levees or shoulders of a four-lane highway. Those few sites where the transition zone approximates natural conditions ( large tracts of marsh with adjacent wildlands like the Petaluma River marsh, the Suisun marshes, and Don Edwards San Francisco Bay National Wildlife Refuge) have become all the more valuable to the remaining populations of black rails.

Under the auspices of the National Biological Survey we conducted a follow-up study in 1996 to try to determine the stability of black rail populations at selected marshes. Our findings were mixed. We had similar to slightly higher detection rates in San Pablo Bay and Suisun marshes. However, none of the marshes that had been "empty" in the earlier study were colonized in the ensuing years. Some of the more isolated, outlying marshes showed declines. The population, therefore, appears to be stable at some of the "core" sites, but possibly declining at the margins.