Asynchrony in recruitment and survivorship in populations located within the potential range of dispersal generally facilitates metapopulation processes' playing an important role in the demographic "rescue" of populations. Conversely, populations that are demographically synchronous over large geographic areas may be particularly vulnerable to the detrimental effects of habitat fragmentation because such synchrony is probably maintained largely by dispersal. To examine the potential generality of such processes, I investigated spatial autocorrelation in annual relative density of California land birds using data from the Breeding Bird Survey and the Christmas Bird Count. Of 88 species I examined using Breeding Bird Survey data, 87 (99%) exhibited no significant spatial autocorrelation at any distance category. Of 79 species I examined using Christmas Bird Count data, 66% exhibited no significant spatial autocorrelation. These results suggest that demographic processes are often asynchronous over relatively short geographical distances and thus that metapopulation processes may be significant for a large fraction of terrestrial bird species. No species during the breeding season, but a small proportion during the winter, were significantly spatially autocorrelated at all geographic scales up to the statewide level (500-1200 km). There was no significant relationship between spatial autocorrelation during the winter and either body size, clutch size, or diet, but migratory species were more spatially autocorrelated than resident species. Spatial autocorrelation in the winter was also related to breeding habitat preferences, with species inhabiting savanna and woodlands (especially oak woodlands) exhibiting lower spatial autocorrelation and those inhabiting subalpine forest exhibiting greater spatial autocorrelation than other species.
