Abstract

Fragmentation of forests in the eastern United States is strongly suspected to have led to the decline of forest bird populations. A similar trend may be occurring in the rangelands of coastal California. Rangelands have been fragmented by exurban development, with its houses, other structures, and landscaping.

A prime concern in fragmentation is the creation of edge habitat. Edges favor the activities of nest parasites and nest predators. The buildings associated with rangeland development harbor mammalian nest predators such as striped skunks, raccoons, Virginia opossums, and domestic and feral cats. The vegetation and structures also attract avian nest predators, especially American crows and scrub jays.

Analysis of historical aerial photographs of Sonoma County demonstrates the invasion of range and pasture lands by exurban residences. Sample sites show the decline of range and pasture areas, and the increase in density of residences and other buildings and associated vegetation. The trend in California is toward increasing human densities in rural landscapes. Conservation of rangeland birds may depend upon directing development to less-sensitive sites, and upon landscaping and construction that are less favorable to predators.

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