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, Howeet 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 (Zembalet al. 1988). Thus, the population dynamics of Belding's Savannah Sparrow may reflect the effects of fragmentation.
