The California brown pelican's listing history is complex. It was listed as an endangered in 1970 as part of the brown pelican species. The 1985 delisting of the "southeast brown pelican" left a single listed entitity including the California brown pelican (P. o. californicus), the Caribbean brown pelican (P. o. occidentalis), and the Mississippi, Louisiana and Texas population of the eastern brown pelican (P. o. carolinensis). Logically, the listed entity should be split into the Western Gulf distinct population segment (MS, LA, TX population of P. o. carolinensis), the Caribbean brown pelican and the California brown pelican.

The California brown pelican population in California declined from 1,125 to 727 annual nests between 1969 and 1970, the year it was placed on the endangered list [1]. With the exception of 1974, the population remained at low levels through 1978 when it reached a low of 466 nests. Between 1979 and 1987 the population rose rapidly to 7,900 nests. Between then and 2004, the it fluctuated around a mean of about 5,000 nests. In 2004, there were 6,000 nests [2]. The fluctuation may indicate that it is at carrying capacity in the Channel Island. As the population increased, the breeding range expanded. A small number of birds has nested at the Salton Sea in most years since 1996.

Historically, breeding colonies of the Brown Pelican were found at Pt. Lobos in
Monterey County up until 1959, and also throughout the Channel Islands and Baja California. In the 1960’s, however, Brown Pelican populations off the coast of Los Angeles began experiencing reproductive failure and by the 1970s, the Brown Pelican was near extinction. The cause of the population decline and the threat of extinction was DDT, which caused egg shell thinning of 35% in some populations. This finding perplexed many environmental scientists and ecologists, for an urbanized area such as Los Angeles does not use DDT nearly as much as agricultural areas. While agricultural runoff was a suspected source of pollution, the source of DDT and its residues came from a factory in the Los Angeles area which was discharging 200 - 500 kg of DDT everyday- equal to 100 tons of DDT pollution per year! Further studies on marine sediments showed that DDT pollution first began appearing in the Los Angeles area in 1952, demonstrating how there is often a time lag between the actual onset of pollution and its negative impacts on the environment.

[1] Shields, M. 2002. Brown Pelican (Pelecanus occidentalis). In The Birds of North America, No. 609 (A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
[2] Rogers, T. 2004. Spate of juvenile deaths follows breeding success. San Diego Union Tribune, August 1, 2004.