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

Changes in local environmental conditions can cause shifts in the dist ribution of nonbreeding shorebirds at sites that offer a wide choice o f habitats. We assessed effects of water level-related variables and s alinity on the distribution of nonbreeding American Avocets (Recurviro stra americana) among eight brackish water impoundments and two intert idal mudflats in coastal South Carolina from mid-January to mid-May, 1 991 and 1992. Avocets exhibited nonrandom distribution on three spatia l scales: between impoundments and natural tidal areas (impoundment us e was greater), among impoundments, and within impoundments. Among all sites, avocet distribution correlated with water level-related variab les (P < 0.05), but not salinity. Most avocets used habitats with wate r 10-17 cm deep and little or no exposed substrate. Furthermore, avoce t numbers decreased in impoundments when the sites experienced large f luctuations in water levels (+/-6-10 cm). Analyses conducted at the le vel of one impoundment supported these results, indicating that macro- (among impoundments) and microhabitat (within impoundments) use was i nfluenced by similar factors.