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Reproductive Success of Belding's Savannah Sparrows in a Highly Fragmented Landscape

Abby N. Powell and Christine L. Collier

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Habitat fragmentation can influence the abundance and distribution of birds. Decreases in patch size increase the amount of edge habitat, which can allow greater invasion by exotic species, predators, and brood parasites (Hagan and Johnston 1992, Donovan et al. 1995). Fragmented habitats may act as population sinks and result in local extinctions unless immigration occurs from source habitats (Pulliam 1988, Howe et al. 1991, Pulliam et al. 1992, Stacey and Taper 1992).

Fragmentation is especially severe in coastal California, where about 75% of the presettlement acreage of coastal wetlands has been lost to development (Zedler 1982, Zedler and Powell 1993). This degradation has produced a highly fragmented landscape that may have a negative influence on the Belding's Savannah Sparrow (Passerculus sandwichensis beldingi), which is one of two wetland-dependent bird species endemic to coastal salt marshes in southern California. This nonmigratory subspecies is listed as endangered by the State of California. Statewide censuses of Belding's Savannah Sparrows reveal wide fluctuations in local population sizes, with local extinctions occurring in some years (Zembal et al. 1988). Thus, the population dynamic's of Belding's Savannah Sparrow may reflect the effects of fragmentation.

Belding's Savannah Sparrows prefer to nest in the mid- to upper-littoral zones of coastal salt marshes, but the effects of habitat characteristics on reproductive success have not been explored (Massey 1979, Powell 1993). Based on geographic variation in song, Bradley (1994) suggested that populations are highly isolated and have low dispersal, but no study has examined immigration and emigration directly. The objectives of our study were to: (1) examine the effects of fragmentation on resident populations of sparrows, (2) examine the influence of habitat on reproductive success, (3) identify characteristics of breeding habitat, and (4) discuss implications of our results for wetland conservation.

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Table of Contents

• Study Area and Methods
• Results
• Discussion
• Conservation Implications
• Acknowledgments
• Literature Cited

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Abby N. Powell* and Christine L. Collier, U.S. Geological Survey, California Science Center, and Department of Biology, San Diego State University, San Diego, California 92182, USA.

*Present address: U.S. Geological Survey, Biological Resources Division, Northern Prairie Wildlife Research Center, Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA.  E-mail: abby_powell@usgs.gov.

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This resource is based on the following source (Northern Prairie Publication 1045):

Collier, Christine L., Powell, Abby N.  1998.  Reproductive Success of Belding's Savannah Sparrows in a Highly Fragmented Landscape.  The Auk 115(2):508-513.  6 pages.

This resource should be cited as:

Collier, Christine L., Powell, Abby N.  1998.  Reproductive Success of Belding's Savannah Sparrows in a Highly Fragmented Landscape.  The Auk 115(2):508-513.  Jamestown, ND: Northern Prairie Wildlife Research Center Online.  http://www.npwrc.usgs.gov/resource/birds/belding/index.htm (Version 18MAY98).

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