Shorebird distributions on ocean beaches of northern california

Use of coastal beaches by nonbreeding shorebirds along the Pacific coast of North America is poorly understood because survey efforts have targeted large bays and wetlands where birds concentrate. Consequently, we studied coastal shorebird distributions and community composition by conducting monthly surveys at 40, 0.5-km linear plots along sandy beaches of coastal northern California from January through April 1996. We recorded 12 species, whose ranked abundances were consistent between winter (January–February) and spring (March–April). However, five of the six commonest species were more abundant in winter than spring. Among beaches, we detected a mean of 2.6 ± 2.3 (SD; range: 0–9) species and 12.0 ± 14.1 (range: 0–62) individuals. Number of species correlated positively with total shorebird abundance. Most species' abundances varied greatly among sites; nine taxa had aggregated spatial distributions, one species was hyper-dispersed, and two species were randomly distributed among beaches. Species composition of the shorebird community was highly nested, partly because abundant species were more widespread in their occurrence than less-numerous taxa. More species and individuals occurred at sites near Humboldt Bay, probably because high tides forced birds off their principal feeding areas within the bay to adjacent beaches. Variation in shorebird use of beaches suggests that some areas are more important to wintering and migrating shorebirds than other locations. Although current levels of human activity in coastal northern California do not appear to influence distributions of nonbreeding shorebirds, we suggest that monitoring and management plans be considered to minimize potential negative impacts of recreational activities, which are certain to increase with human population size and recreational use of beaches.