Food‐Habitat Relationship of Sea Ducks on the New Hampshire Coastline

Abstract

Use of habitat, food preferences, and food availability were studied for seven species of waterfowl (white—winged scoter (Melanitta deglandi), surf scoter (M. perspicillata), common scoter (Oidemia nigra), oldsquaw (Clangula hyemalis), common goldeneye (Bucephala clangula), bufflehead (B. albeola), and red—breasted merganser (Mergus serrator)) on a 34—km section of the New England coastline during 1968—70. The three scoters selectively used areas of sandy substrate and had very similar food habits. The principal foods were the Atlantic razor clam (Siliqua costata) and Arctic wedge clam (Mesodesma arctatum), which were characteristic of, and abundant in, sandy substrate. In contrast to scoters, goldeneye preferred areas of rocky substrate associated with rocky headlands. They fed primarily on amphipods, isopods, crabs, and gastropods, which were commonly found in the Irish moss (Chondrus crispus) covering of the rocky sublittoral areas. Red—breasted mergansers, like goldeneye, also used the rocky areas. They fed primarily on several small fish species that were observed among the Irish moss and crevices of the rocky substrate. Bufflehead had the most restrictive distribution, being confined mostly to estuaries. Bufflehead fed primarily on sand shrimp, which were found only in harbors with soft ooze bottoms. Oldsquaw had the most generalized diet of all the sea ducks. The major food items consisted of bivalves, gastropods, sand shrimp, and isopods, which were found throughout the study area and accounted for the generalized distribution of oldsquaw along the coastline and in the harbors. Sea ducks were concentrated near the mouths of the estuaries, where more abundant food resources particularly bivalves, were found. Although the species vary, the types of foods eaten by sea ducks were similar to those described in other studies. Thus, food availability, coupled with the physical structure of the substratum in the different coastal habitats, is apparently a major determinant in the way that coastal waterfowl selectively use habitat types. The described patterns of habitat usage appear to have implications for other wide geographical areas.