Abstract

Extensive habitat loss and degradation have resulted in decreases in populations of tidal marsh breeding birds in the San Francisco Estuary in the past 150 years. We conducted point count surveys and nest monitoring in tidal marsh habitat at China Camp State Park from 1996 through 2007 to assess bird abundance, species richness and reproductive success over time. We found overall species richness at China Camp to be significantly lower than that of other San Pablo Bay tidal marshes, but also to be increasing during the study period. We present relative density indices and confirm breeding for three focal species that are of conservation concern: San Pablo song sparrow (Melospiza melodia samuelis), California black rail (Laterallus jamaicensis coturniculus), and California clapper rail (Rallus longirostris obsoletus). Song sparrows were observed at higher densities at China Camp than at other San Pablo Bay sites. There was no apparent trend in song sparrow density during the study period at China Camp, in contrast with the rest of San Pablo Bay, which displayed a significant decline. We determined song sparrow nest survival probability using the method described by Mayfield (1975) and found that nest survival at China Camp varied markedly among years, from >30% in 1996 to 6% in 2006, with no discernible trend. The main causes of nest failure were predation and tidal flooding. Song sparrow nests were found predominantly in gumplant (Grindelia stricta) and pickleweed (Sarcocornia pacifica) and less commonly in saltgrass (Distichlis spicata). Clapper rails nested exclusively in pickleweed and black rail nests were found mainly in gumplant and less commonly in saltgrass. China Camp’s expansive ancient marsh supports endemic and bird species of conservation concern, while serving as a reference site for tidal marsh studies in San Francisco Bay. The long-term monitoring of tidal marsh bird breeding parameters at China Camp has the potential to provide early detection of declining population trends before local populations become imperiled.

Highlights

  • Tidal salt marsh is critical habitat for the persistence of many bird species (Burger 1985) and supportsSAN FRANCISCO ESTUARY & WATERSHED SCIENCE many endemic species or subspecies (Greenberg and Maldonado 2006)

  • North America supports the highest number of terrestrial vertebrate species with subspecies endemic to tidal salt marsh (Greenberg and Maldonado 2006), and birds compose the majority of these endemic subspecies

  • Song sparrows were the most common species breeding at China Camp, with fewer nests found for black rail and clapper rail

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Summary

Introduction

SAN FRANCISCO ESTUARY & WATERSHED SCIENCE many endemic species or subspecies (Greenberg and Maldonado 2006). North America supports the highest number of terrestrial vertebrate species with subspecies endemic to tidal salt marsh (Greenberg and Maldonado 2006), and birds compose the majority of these endemic subspecies. Other endemic subspecies include the following State of California Bird Species of Special Concern: the San Francisco common yellowthroat, and three subspecies of song sparrow: Suisun song sparrow (Melospiza melodia maxillaris), Scientific name Aechmophorus occidentalis Aechmophorus clarkii Ardea herodias Ardea alba Egretta thula Cathartes aura Branta canadensis Anas strepera Anas americana Anas platyrhynchos Aythya affinis Oxyura jamaicensis Pandion haliaetus Elanus leucurus Circus cyaneus Buteo lineatus Buteo jamaicensis Laterallus jamaicensis coturniculus Rallus longirostris obsoletus Rallus limicola Charadrius vociferus Himantopus mexicanus Tringa melanoleuca Catoptrophorus semipalmatus

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