Migrant shorebirds at Sandy beaches located between two major wetlands on the Pacific Coast of Baja California (Mexico)

In this paper we describe the composition and abundance of shorebirds at two sandy beaches located north and south of Punta Cabra (Baja California, Mexico). These beaches are located halfway between two coastal lagoons that are important along the Pacific Flyway (estero Punta Banda and San Quintin bay, 180 km apart). Scarcity of coastal lagoons in Baja California triggered our interest in documenting shorebird migration in the absence of major wetlands. We conducted 23 censuses biweekly from September 1990 through October 1991. Nineteen shorebird species and 1,127 individuals were recorded. The sanderling (Calidris alba) was the most abundant species at both beaches. Chi-square tests showed significant differences in the abundance of whimbrel (Numenius phaeopux), snowy plover (Charadrius alexandrinus), and the surfbird (Aphriza virgata) between beaches. Peaks of abundance were dominated by three or fewer species. There were differences between beaches in the time of occurrence of the peaks, and in species composition. Removal of the dominant species in the analysis of similarity revealed differences between beaches and showed that both are important to the shorebird assemblage. Our findings suggest that open beaches are important for the sanderling and the snowy plover. Species recorded at Punta Cabra but not at estero Punta Banda can be explained by unique habitat features such as rock outcrops next to the beaches, sandy beaches where kelp (Macrocystis) has washed ashore, and natural vegetation near the beaches. Sandy beaches provided migration habitat for species previously recorded only at flats in the region. Differences found in this study indicate that the importance of small sites deserves further investigation in coastal areas where major wetlands are scarce or far apart. Conservation of Punta Cabra at a regional level should be considered in shorebird protection programs