The relationship between size, caloric content, and association of prey fishes in meals that adult Rhinoceros Auklets (Cerorhinca monocerata) carry to their nestlings was studied on Pine and Triangle Islands, British Columbia from 1977 to 1979. Rhinoceros Auklets carried wide fishes widthwise in their bills and slender fishes by their height or width. The number of fish carried per trip was inversely related to their size. The longest fishes made up the largest meals in biomass and provided most energy to the nestlings. Four large species, Pacific saury (Cololabis saira), second-year Pacific herring (Clupea harengus), second-year Pacific sandlance (Ammodytes hexapterus), and bluethroat argentine (Nansenia candida), were negatively associated with other prey fishes. Small fishes of different species were positively associated with one another in meals, as well as certain small fishes with larger ones, but not vice versa. By com- plementing small fishes of one species with fishes of other species, foraging Rhinoc- eros Auklets boosted the energy content of a meal. Total food consumption of nestling Rhinoceros Auklets in the northeastern Pacific was estimated at 326 metric tons or 1.7 billion kcal per nesting season. Comparison of caloric intake among nestling Rhinoc- eros Auklets, Cassin's Auklets (Ptychoramphus aleuticus), and Tufted Puffins (Fratercula cirrhata) revealed that smaller alcids take in more calories per gram body weight than larger ones. The Rhinoceros Auklet (Cerorhinca monocerata) belongs to the puffins (Storer 1945), a group of alcids that carry fishes crosswise in their beaks to their nestlings. There are four species of puffins: the Atlantic Puffin (Fratercula arctica) in the North Atlantic Ocean, and the Tufted Puffin (F. cirrhata), Horned Puffin (F. corniculata), and Rhinoceros Auklet in the North Pacific Ocean. In contrast to the other puffin species that visit their nest sites several times each day, nestling Rhinoceros Auklets receive two meals, one from each parent, each night (Richardson 1961). A meal is defined here as a bill load of fish carried by an adult bird to its nestling. The auklets can be relatively easily captured and their prey collected (Vermeer and Westrheim 1984). The diet of nestling Rhinoceros Auklets in British Columbia consists of at least 27 species of juvenile fish and 2 squid species. Pacific sandlance (Ammodytes hexapterus), Pacific herring (Clupea harengus), Pa- cific saury (Cololabis saira), several rockfish (Sebastes spp.), and sockeye salmon (Oncho- rhynchus nerka) are the most common fish species consumed (Vermeer and Westrheim 1984). Vermeer and Westrheim (1984) also noted within-season and between-year changes in age and size of prey species, and noted differences in prey composition between inshore and offshore nesting colonies. They did not, however, report on prey association and caloric content of Rhinoceros Auklet meals. The first objective of this study was to determine the relationship between size, caloric content, and association of prey fishes in meals of nestling Rhinoceros Auklets by ex- amining 1) prey dimensions, including shape, size, and weight of prey species; and 2) the number, length, age class, weight, and caloric content of fishes observed in single- species meals. The second objective was to determine the overall food consumption and caloric intake of nestlings. METHODS