In late summer, the brown pelican heads up the California coast from its breeding and nesting sites on the islands off the coast of Mexico. After four or five months raising their chicks and teaching them the difficult skill of plunge diving, the pelicans follow their food supply - anchovy, sardine and mackerel - as far north as British Columbia. Elkhorn Slough is one of the most important roosting sites along the way, with peak roost counts between 1000 and 5000 birds! Many pelicans arrive during May and June, with the greatest numbers present from July to October.

The Brown Pelican, Pelicanus occidentalis, is an endangered species. At one time, the numbers of Brown Pelicans were greatly diminished because of the overuse of pesticides, such as DDT. These pesticedes reached the ocean in contaminated runoff water and then were absorbed by fish, who carried the pollutants into the food chain. When these pesticide-laden fish were consumed by pelicans, they were greatly affected. Their eggs were too thin to produce healthy chicks. Today, the Brown Pelican is making a comeback with the reduced use of DDT. However, they are still considered endangered. Among the threats that remain are their fluctuating norther anchovy food supply. Humans and dog disturbance of their ground nests is also becoming a problem.