Brown Pelicans in Southern California: Habitat Use and Environmental Fluctuations

The population size, distribution, and habitat affinities of Brown Pelicans (Pelecanus 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 relatively 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 to 94,000 birds occurred in September and October. Throughout autumn and early winter, pelicans regularly occurred as far offshore as Cortés 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 about 30 km of shore. During August and December, however, 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 two-year warming trend on pelican numbers are discussed.