Non-Breeding Shorebird Ecology and Behavior on a Habitat Mosaic in Southeastern U.S.

We studied shorebird diversity, abundance, distribution, and behavior on Bulls Island, South Carolina, a protected and minimally disturbed barrier island on the mid-Atlantic coast of the United States during the non-breeding seasons of 2018 and 2019. We recorded 21 shorebird species on Bulls Island. Average densities of shorebirds ranged from 4102505 birds per linear km of beach throughout the two study seasons. Shorebird species richness was significantly affected by the number of local microhabitats (χ21 = 83.51, P < 0.0001, n = 35) and by number of invertebrate taxa (χ21 = 10.21, P = 0.001). Foraging behavior of four focal species varied across available habitats and both location and rate of foraging were associated with greater invertebrate availability and proximity to other foraging shorebirds. Dunlin (Calidris alpina) exhibited the highest foraging rate compared to Piping Plovers (Charadrius melodus), Semipalmated Plovers (Charadrius semipalmatus) and Sanderling (Calidris alba). Despite some differences between species, foraging rates were highest on marsh relicts and mudflats in March and April, and lowest during high tide in all habitats. Aggressive interactions occurred in 12225% of observations depending on the species and were more frequent in habitats with greater invertebrate availability. Bulls Island, through its mosaic of habitats, provides conditions for a diverse and abundant shorebird community, and thus is an important non-breeding location worthy of further protection.