Abstract: Most closely related sympatric bird species differ in their food-gathering structures, foraging techniques, and/or food preferences, with the result that they take different kinds of foods (Lack, 1954; Newton, 1967). Specialization in diet presumably evolves as a consequence of competition for limited food resources and is considered essential for continued coexistence (Lack, 1954; Mayr, 1963). This type of specialization also reflects the importance of food as an evolutionary factor in natural populations. We have found, however, that the diets of birds breeding on Arctic tundra overlap to a strikingly high degree. The circumstances behind this are straightforward: the overlap is a consequence of a limited taxonomic diversity of food sources and a relatively simple community structure. Neither of these appears to provide, in space or time, the range of opportunities permitting the variety of food specialization observed at temperate latitudes or farther south. The questions then arise, how can high arctic tundra such as that near Point Barrow, Alaska, support the variety and abundance of birds occurring there, and how do the birds' interact with regard to food supply? These are large questions that are continuing foci of research in northern Alaska. Results of an examination of the feeding ecology of tundra birds should also provide insight into two other problems which concern ecologists; namely, how different do diets of two or more species have to be to allow them to live sympatrically, and conversely, what are the consequences, ecologically and behaviorally, when two or more similar species exploit a common food source? This paper focuses on the diets and foodexploitation patterns of four widely sympatric sandpipers of the genus Calidris that breed regularly and abundantly near Barrow, Alaska. These are the red-backed (C. alpina), pectoral (C. melanotos), Baird's (C. bairdii) and semipalmated (C. pusillus) sandpipers. In addition, five other congeners are present occasionally in the Barrow area and can breed there: one is present almost every year, usually sparsely, but in occasional years commonly (C. fuscicollis); the other four are only sporadic or infrequent breeders, occurring in small numbers (canutus, alba, mauri and ferruginea). A sixth (ruficollis) also occurs sporadically and may yet be found to breed. This is the largest group of avian congeners that occurs near Barrow, but its members are not the only insectivores present. Other shorebirds, ducks, gulls, and a few passerines also breeding there take the same general kinds of foods as the sandpipers. Thus, the problems related to sympatry and use of a common food source extend beyond the group of species considered here. But the four common species of Calidris comprise a substantial part of the insectivore fauna in the Barrow area. Given these four variations on a basic theme of structure, physiology and behavior (the genus Calidris) that are regularly and abundantly present on the grass-sedge tundra near Barrow, we seek clues from differences between them as to factors permitting their coexistence. Our immediate objective is to describe diet and to examine degree of overlap.