Use of intertidal habitat by four species of shorebirds in an experimental array of oyster racks, reefs and controls on Delaware Bay, New Jersey: Avoidance of oyster racks

Abstract

Many shorebirds breed in Arctic habitats, and migrate south to wintering quarters in the Southern Hemisphere. Shorebirds mainly forage on intertidal mudflats at low tide. A key spring stopover for shorebirds in North America is Delaware Bay, New Jersey, where shorebirds feed on horseshoe crab (Limulus polyphemus) eggs at high tide. The importance of intertidal to migrant shorebirds has been overlooked. This paper examines foraging of 4 shorebird species at Reeds Beach, Delaware Bay. The intertidal zone was divided into an experimental array with oyster racks, artificial reefs, and controls to quantify the number of birds present in each section. The best models for all species (except sanderling, Calidris alba) explained over 60% of variation in number present as a function of other shorebirds, date, and treatment. Time of day was the only factor affecting the number of sanderlings. Date is a contributing factor because numbers are low in early May, peak by May 20–25th, and decrease in late May as shorebirds leave for the Arctic. Red knots (Calidris canutus rufa), turnstones (Arenaria interpres), and semipalmated sandpipers (Calidris pusilla) were present less often, and in smaller numbers in the oyster rack treatment (compared to the other treatments). There was a high association between foraging species. The data clearly show avoidance of the oyster racks by knots, turnstones and semipalmated sandpipers, but they did not avoid those with reefs or the control. These results are important because of the desire to expand aquaculture along the Delaware Bay into prime shorebird foraging areas. The Precautionary Principle dictates that the expansion of intertidal oyster culture be halted in areas of high foraging value for red knots (threatened in the U.S.) and other shorebirds until any effects on fitness are determined.