Influence of Abiotic Factors and Prey Distribution on Diet and Reproductive Success of Three Seabird Species in Alaska

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Abstract
Seabirds are suggested as useful indicators of the abundance and distribution of various of their prey species as well as indicators of changes in oceanic conditions. Additionally, it is shown that seabirds with varying foraging methods are affected differently, with respect to breeding success, by changes in prey numbers and availability. Diets of three seabird species changed dramatically over a two-year period (1977 to 1078) with respect to numbers, species, frequency of occurrence, and length of prey. A concomitant reduction in breeding success from 1977 to 1978 (by up to 90%), was noted for surface-feeding Black-legged Kittiwakes Rissa tridactyla and Glaucouswinged Gulls Larus glaucescens, but not for diving Tufted Puffins Fratercula cirrhata. Concurrent sampling of fish prey populations revealed stratification and depression of stocks in 1978 of the predominant species eaten in 1977. Possible explantations of changes in fish stocks are lower sea temperatures in 1978 and seawater dilution in 1977.