Brown Pelicans in Southern California: Habitat Use and Environmental Fluctuations

Abstract

The population size, distribution and habitat affinities of brown pelicans (P. occidentalis) were investigated during 1975-1978 using monthly aerial, ship and ground surveys throughout the southern California bight. Pelican numbers are lowest during spring, when most birds are found near the small nesting colonies at Anacapa Island and Islas Los Coronados. The annual post-breeding migration from Mexican colonies augments the local population during summer and autumn; estimated peak populations of 65,000-94,000 birds occurred in Sept. and Oct. Throughout autumn and early winter, pelicans regularly occurred as far offshore as Cortes Bank, 75 km seaward from the nearest island and 175 km off the mainland. Adults predominated offshore and near the California Channel Islands all year, but immature birds outnumbered adults along the mainland shore during autumn and winter. Brown pelicans occurred at sea in highest densities in areas of shallow, warm water within .apprx. 30 km of shore. During Aug. and Dec., migrating birds showed no discernible affinity for particular sets of environmental conditions. The distribution of spawning northern anchovies, the principal prey of brown pelicans during the nesting season, was not a good indicator of bird density distribution. The effects of a 2-yr warming trend on pelican numbers are discussed.