BROWN PELICAN POPULATIONS AND POLLUTANTS IN TEXAS 1975-1981

摘要: Only a decade ago the population of Brown Pelicans (Pelecanus occidentalis) nesting in Texas was considered nonviable. From mid- 1950s through 1974 no more than 50 pelicans remained from that once numbered about 5000 individuals. During those years, there were few attempts at reproduction, and seldom produced enough young to compensate for adult mortality. The history, status, role pesticides decline this endangered species on Gulf Coast early 1 960s reviewed an earlier paper (King et al. 1977). Our studies since indicate reproductive success has improved is increasing. purpose present data gathered 1975 1981 environmental contaminants interpret contaminant influence current Pelican status. We made year-round observations known habitats coastal document numbers wintering birds. Weekly throughout season onset courtship fledging. observed colonies distance least 200 m minimize effects human disturbance. 1979, areas not entered until most birds had been incubating 2-3 weeks. In 1980 1981, we did approach individual nests could be seen with aid binoculars. then examined unhatched eggs assess viability. Abandoned collected analysis residues measure shell thicknesses. Whole weighed measured. contents removed, frozen, stored chemically cleaned jars. Shell thicknesses compared museum before widespread use DDT (pre- 1947), also, measurements 1970 reported by King (1977). used comparisons thickness. Because only addled abandoned residue analyses thickness, our collection random sample. Pollutant may have biased towards higher levels, shell-thickness values lower obtained viable eggs. Nestling banded color-marked just prior Each pelican Fish Wildlife Service band one leg rigid, colored, plastic other leg. Colored bands coded year but colony which fledged. study, two monrbund recovered Corpus Christi Bay. Both died within 24 h capture despite concerted efforts keep them alive.