Responses of Three Seabird Species to El Nino Events and Other Warm Episodes on the Washington Coast, 1979-1990

Abstract

For 1979-1990, I compared satellite-based sea surface temperature anomaly data for Washington's outer coast with the annual number of nests of Double-crested Cormorants (Phalacrocorax auritus) and Brandt's Cormorants (Phalacrocorax penicillatus), and the number of Common Murres (Uria aalge). Sea surface temperatures were a minimum of 1°C above average for at least four consecutive months during three periods: January-April 1981, February-June 1983, and September 1987-February 1988. The first warm event was not associated with El Niño, while the second and third warm episodes were the results of a severe (1982-1983) and more moderate (1987) El Niño events. Numbers of the three seabird species were significantly negatively correlated with the intensity and occurrence of these warm events, although the effects of the 1981 event were not clear-cut. Cormorant nesting was depressed during El Niño and post-El Niño years. Differences in response of the two cormorant species may be related to differences in their breeding chronologies. In 1983, murres crashed to 13% of pre-1983 levels. With the exception of 1987, numbers remained at this level through 1990. The interpretation of ENSO effects on murres is complicated by several types of human disturbance.