Kelly, J. P., Etienne, K. L., Roth, J. E.,
During the breeding season of 1999, we surveyed from roads in the San Francisco Bay area to determine the regional abundance and distribution of the Common Raven (Corvus corax) and American Crow (C. brachyrhynchos). Ravens Concentrated along the outer coast and occurred in relatively low numbers in some Interior areas, where as the number of crows increased significantly from the outer coast to interior and bayshore locations. Both species occurred in significantly greater densities along urban and suburban survey routes than along rural routes, but dramatic exceptions were evident in some areas. Data from Breeding Bird Surveys, Christmas Bird Counts, and breeding bird atlases yielded similar distribution patterns. Breeding Bird Surveys and Christmas Bird Counts revealed strong regional increases in both Species, but annual trends varied substantially at local scales. This variation, as well as significant abundance variation among survey routes, suggested considerable local differences in either habitat suitability or capacity for further population growth. Our results suggested that raven and crow populations may increase in both rural and developed areas undergoing rapid urbanization and that local conditions, rather than whether the habitat is rural or urban, may influence regional patterns.
Kelly, J. P., K. L. Etienne, and J. E. Roth. 2002. Abundance and distribution of the Common Raven and American Crow in the San Francisco Bay area, California. Western Birds 33: 202-217.