HABITAT-RELATED FACTORS AFFECTING THE DISTRIBUTION OF NONBREEDING AMERICAN AVOCETS IN COASTAL SOUTH-CAROLINA

Changes in local environmental conditions can cause shifts in the distribution of nonbreeding shorebirds at sites that offer a wide choice of habitats. We assessed effects of water level-related variables and salinity on the distribution of nonbreeding American Avocets (Recurvirostra americana) among eight brackish water impoundments and two intertidal mudflats in coastal South Carolina from mid-January to mid-May, 1991 and 1992. Avocets exhibited nonrandom distribution on three spatial scales: between impoundments and natural tidal areas (impoundment use was greater), among impoundments, and within impoundments. Among all sites, avocet distribution correlated with water level-related variables (P < 0.05), but not salinity. Most avocets used habitats with water 10-17 cm deep and little or no exposed substrate. Furthermore, avocet numbers decreased in impoundments when the sites experienced large fluctuations in water levels (+/-6-10 cm). Analyses conducted at the level of one impoundment supported these results, indicating that macro- (among impoundments) and microhabitat (within impoundments) use was influenced by similar factors.