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Rail Mystery

Clapper rail numbers have crashed in some unexpected locations around the Bay, according to surveys of this secretive, short-tailed denizen of the salt marsh. Recent field studies reveal that rails in the more pristine North Bay marshes are faring less well than those in urbanized areas. The estimated 13 pairs present at Sonoma Creek in 1993 dropped to between just 1 and 3 pairs in 1998, and in 2001, no rails were found. In the White Slough marshes along the Napa River, an estimated 16-24 pairs surveyed in the 1990s dropped to 4 to 7 pairs in 2001, and the count may be even lower this year, according to rail expert Jules Evens, who headed up the surveys.

Ironically, the rail seems to be doing better in some of the Central and South Bay marshes, where their numbers have remained fairly stable over the past several years, according to Evens, and may even be increasing in places like the San Bruno Marsh and the San Leandro shoreline.

Since rails aren’t known for their love of human proximity, what explains this surprising phenomenon? One theory, says Evens, is that there are more predators in the North Bay marshes: red foxes, mink, rats, and feral cats have all been spotted there. In the more urban sites, says Evens, these predators may not have as much of a refuge. Some of the urban sites have implemented predator control programs, which appear to be helping the rails: the rails made a comeback at the Don Edwards National Wildlife Refuge after such a program was put in place. Other potential problems in the North Bay include construction taking place adjacent to the marshes, and hydrological changes—such as late spring rains—that may be "freshening" the marsh. That theory is bolstered by the fact that Virginia rails, which prefer fresher conditions, appear to be increasing in the White Slough marshes, according to Evens.

While human activities at the urban sites likely affect rail breeding success and mortality too, he explains, those activities are not having the same scale of impact the predators are.

"Red fox in particular seem to key on marshes and are very efficient at finding and destroying nests and probably breeding adults," says Evens. LOV

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