Factors affecting reproductive success of the California clapper rail (Rallus longirostris obsoletus) in San Francisco Bay

Metadata Updated: May 19, 2018

We assessed the reproductive success of the California clapper rail (Rallus longirostris obsoletus), an endangered species restricted to San Francisco Bay, and the relative importance of predation, flooding and contaminants as factors affecting that success. Our study was conducted in six tidal marshes in both the north and south reaches of San Francisco Bay. This assessment, conducted over a period of 4 years (1991, 1992, 1998, 1999), determined that fecundity of clapper rails was much reduced over the natural potential. Only 69 percent of clapper rail eggs whose viability could be assessed were viable. Rail egg hatchability in north and south bay marshes was 65 percent and 70 percent respectively. Only 45 percent of the nests successfully hatched at least one egg. Despite mean clutch sizes of 6.66 and 6.94 in the north and south bays respectively, clapper rails produced only 1.9 and 2.45 young per nesting attempt. Flooding was a minor factor in reducing fecundity, accounting for only 2.3 percent of eggs lost. Predation was a major factor in reducing nest success and accounted for one-third of the eggs lost. Failed clapper rail eggs were collected for embryo examination and chemical analysis of trace elements and organochlorines. Contamination appeared to exert an adverse influence over clapper rail reproductive success as evidenced by observations of deformities, embryo hemorrhaging, embryo malpositions, a depressed rate of hatchability, the exceedance of avian embryotoxic threshold concentrations for mercury, barium and chromium in some eggs, and the correlation of deformities with elevated concentrations of trace elements in fail-to-hatch rail eggs. While all marshes had impaired hatchability, the marshes with the lowest rate of hatchability were those adjacent to potential contaminant sources. Mercury was the only significant contaminant common to all marshes. Mercury concentrations exceeded the LOAEC of 0.5 ug/g on a fresh wet weight basis in at least some failed eggs in every marsh sampled. Mercury concentrations in failed clapper rail eggs in the south and north bays were 0.54 ug/g and 0.36 ug/g, respectively, and ranged from 0.17 to 2.52 ug/g in the south and from 0.11 to 0.87 ug/g in the north bay.

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Public: This dataset is intended for public access and use. License: No license information was provided. If this work was prepared by an officer or employee of the United States government as part of that person's official duties it is considered a U.S. Government Work.

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Metadata Created Date May 19, 2018
Metadata Updated Date May 19, 2018

Metadata Source

Harvested from doi.data.json

Additional Metadata

Resource Type Dataset
Metadata Created Date May 19, 2018
Metadata Updated Date May 19, 2018
Publisher Fish and Wildlife Service
Unique Identifier FWS_ServCat_23193
Brent Frakes
Maintainer Email
Public Access Level public
Bureau Code 010:18
Metadata Context https://project-open-data.cio.gov/v1.1/schema/catalog.jsonld
Schema Version https://project-open-data.cio.gov/v1.1/schema
Catalog Describedby https://project-open-data.cio.gov/v1.1/schema/catalog.json
Data Quality True
Harvest Object Id e97eda45-23cb-44bc-8f57-b7f8252da5cf
Harvest Source Id 6b50978a-7573-455a-91db-55a923988900
Harvest Source Title doi.data.json
Data First Published 2003-07-01
Homepage URL https://ecos.fws.gov/ServCat/Reference/Profile/23193
Data Last Modified 2017-11-01T22:11:57.891075
Program Code 010:094, 010:028
Related Documents https://ecos.fws.gov/ServCat/Reference/Profile/23193
Source Datajson Identifier True
Source Hash 1e45e12a6766c2f3ac18253f15e1949e386d4927
Source Schema Version 1.1
Spatial -122.2514,37.41263,-121.9237,37.6908
Category Unpublished Report

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