Before 1920, native populations of brown pelicans (Pelecanus occidentalis carolinensis) were estimated at 50,000 to 85,000 birds in Louisiana and 5,000 in Texas. By 1958, brown pelicans had vanished from two wintering areas in each state, and wintering and breeding birds disappeared from additional areas between 1959 and 1961. By 1963, the disappearance of the brown pelican from Louisiana was complete, and in Texas only about 100 birds were observed annually. Mortality before 1939, particularly in Texas, was attributed mostly to hunters and fishermen. Losses in both states were attributed to hurricanes, disease, and extended periods of freezing weather. Pesticides may also have contributed significantly. Widespread endrin-caused fish mortality was documented between 1958 and 1964 in Louisiana. Pelicans undoubtedly were exposed to endrine through eating the fish. Significant levels of DDE were found in Texas fishes in the late 1960's. DDE residues in pelican eggs were high enough to be responsible for nesting failure. Shell thinning averaged 10% in Texas pelican eggs collected in 1970, 1972, and 1974, but in earlier years greater thinning was associated with the collapse and loss of eggs. Poor reproductive success during recent years was believed due to (1) failure of many adult pelicans to nest and (2) a high rate of nestling mortality in the few pairs that did nest and hatch young. The remnant population of brown pelicans on the Texas Coast will disappear unless reproductive success improves, because recruitment is presently insufficient to offset mortality.
