Environmental and Habitat Correlates of Pasture Use by Nonbreeding Shorebirds

Abstract

Throughout coastal regions of the world, pasturelands often augment important and declining intertidal foraging habitats for nonbreeding shorebirds (Suborder Charadrii). Little is known, however, about factors influencing bird use of pastures. Hence, we examined the spatial distribution of shorebirds in coastal pastures near Humboldt Bay, California from October 1991-May 1992 and correlated spatial distribution patterns with environmental and habitat variables. Shorebirds used pastures in a nonrandom (clumped) fashion. Pasture use varied seasonally for Killdeer (Charadrius vociferus), Marbled Godwit (Limosa fedoa), and Common Snipe (Gallinago gallinago); Dunlin (Calidris alpina) and Black-bellied Plover (Pluvialis squatarola) use increased when it rained, and Dunlin, Black-bellied Plover, and Killdeer use increased nearer the time of a new moon. At the level of the individual pasture, the likelihood of encountering most species (5 of 6) increased as vegetation height decreased. The likelihood of pasture use by Dunlin and Killdeer increased when shorebirds used pastures the previous week. Extensive, nonrandom use of coastal pastures by nonbreeding shorebirds indicates that conservation planning for shorebirds should consider habitat characteristics. In the vicinity of Humboldt Bay and other coastal bays, use of pastures by shorebirds can be increased by practices that provide short vegetation. Although shorebird use did not correlate with use of pastures by cattle, grazing by livestock is probably the means by which to achieve habitat characteristics attractive to shorebirds while maintaining compatible human uses on private lands. Regular use of some pastures by shorebirds indicates that site faithfulness may be important and that "traditional" sites need to be identified and protected.