Breeding performance of black-legged kittiwakes in relation to food availability: a controlled feeding experiment. Black-legged kittiwakes (Rissa tridactyla) at many colonies in Alaska are failing chronically to reproduce. On Middleton Island (north-central Gulf of Alaska), for example, breeding has been a total or near total failure in 13 of the last 15 years. Formerly one of the largest aggregations of kittiwakes anywhere in the world, this colony has declined about 75% since 1981. Low productivity of Alaskan kittiwakes contrasts sharply with this species' performance in some areas of the North Atlantic, where annual productivities in excess of 1 chick per pair are normal. Annual productivity on Middleton since 1983 has averaged less than 0.1 chicks per pair. Circumstantial evidence points to a deficient food supply as the cause of poor productivity in Alaskan Kittiwakes. In a review of kittiwake breeding performance throughout the North Pacific, Hatch et al. (1993) determined that, on average, egg production (or the absence of it) accounted for half of the unrealized potential for fledged young in a typical colony and year. When colonies failed (fewer than 0.1 chicks fledged per pair), two-thirds of their potential productivity was lost through a combination of nonbreeding and reduced clutch sizes. The authors concluded that kittiwake productivity in Alaska is limited primarily by the inability of many pairs to produce eggs, and secondarily by their poor success at hatching eggs and rearing chicks. At Middleton Island, kittiwakes nest on an artificial structure (an abandoned radar tower) which, with various enhancements accomplished in the years leading up to this study, offers a breeding group uniquely accessible for observation and experimental manipulation. In 1994, this colony was augmented by adding some 200 wooden ledges to the walls of the tower and replacing the deteriorating inner wallboard with plywood paneling. In 1995-1996, sliding one-way glass windows were installed behind 144 nest sites as well as feeding tubes that permit the presentation of suitable food (e.g. thawed bait fish) to breeding adults and their chicks. As needed, individuals can be captured on their ledges and pulled into the building for banding, weights and measures, food sampling, or other handling. Against this biological background, and capitalizing on the unique features and accessibility of the experimental colony, this study is designed to address three main questions: (1) Is food limitation responsible for chronic breeding failure of kittiwakes on Middleton Island? (2) At what stage or stages of the breeding season (prelaying, egg productions, incubation, or chick-rearing) are the effects of food limitation most evident? (3) Which parameters of breeding performance (laying dates, clutch sizes, hatching success, chick growth, and others) are most sensitive to food supply?