Two field seasons (1970 and 1971) were spent studying the feeding ecology of the ancient murrelet (Synthliboramphus antiquus) and the marbled murrelet (Brachyramphus marmoratus) near Langara Island, Queen Charlotte Islands, British Columbia. The relatively offshore-feeding ancient murrelet nests in colonies, lays two-egg clutches, and has truly precocial young. The inshore-feeding marbled murrelet is apparently a solitary nester, has one-egg clutches, and semiprecocial young. The ancient murrelet feeds predominantly on two species of euphausiid crustaceans, Euphausia pacifica and Thysanöessa spinifera, during the early portion of the terrestrial phase of its breeding cycle (early April to late May), but takes a fish, Ammodytes hexapterus, toward the end of the cycle. It is believed that this change in diet as the season progresses reflects a change in prey availability. The apparent patchy distribution of the prey of the ancient murrelet, which requires more time to locate the food source, has probably promoted the evolution of the 72-h incubation shifts found in this species.During the terrestrial phase of the marbled murrelet's breeding cycle (early May to late August), the fish Ammodytes hexapterus and Cymatogaster aggregata are predominantly taken. During the very early part of its breeding season, Thysanöessa spinifera constitutes a considerable part of its diet.