Shorebird Use of Sandy Beaches in Central California

Abstract

In this study, the relationship between physical attributes of sandy beaches, levels of human disturbance, and shorebird occurrence was investigated. The linear density km-1 of shorebirds on 42 km of sandy beaches in Monterey Bay, California was documented from late autumn through spring, and the relationship of shorebird densities to two physical variables (slope of beach swash zone, total beach width), one spatial variable (distance to Elkhorn Slough, a wetland of regional importance for shorebirds), and relative level of human disturbance was analyzed using stepwise multiple regression. The six most abundant species were Sanderling (Calidris alba), Willet (Tringa semipalmata), Marbled Godwit (Limosa fedoa), Black-bellied Plover (Pluvialis squatarola), Whimbrel (Numenius phaeopus) and Snowy Plover (Charadrius alexandrinus). Mean abundance of four of the six most abundant species (Marbled Godwit, Willet, Whimbrel, Black-bellied Plover) was negatively related to swash zone slope; flatter beaches supported more shorebirds. Mean abundance of all species analyzed was negatively related to distance to Elkhorn Slough; beaches closer to the mouth of Elkhorn Slough supported more shorebirds. Total beach width had no effect on shorebird occurrence, and level of human use appeared to have no effect. Most shorebird species were more abundant on beaches at low than at high tide, indicating that sandy beaches provide important foraging habitat regionally.