Recruitment failure in American avocets and black-necked stilts nesting at Kesterson Reservoir, California, 1984-1985

We evaluated recruitment by American Avocets (Recurvirostra americana) and Black-necked Stilts (Himantopus mexicanus) in 1984 and 1985 at the selenium-contaminated Kesterson Reservoir and at a nearby reference site, the Volta Wildlife Area, both in western Merced County, California. Nests were monitored to determine their outcomes, including hatching success, and broods were censused three times per week during the breeding season. Chicks were counted and broods classified according to age. Although large numbers of chicks were presumed to have hatched at Kesterson, only one chick older than about 2 weeks of age was observed there during the 2-year study. It is unlikely that chicks of either species survived to fledging at Kesterson during the study period, whereas one-month-old or older avocet and stilt broods were seen both years at Volta. Selenium occurred at high concentrations in food-chain organisms only at Kesterson and was the most likely cause of the recruitment failure of stilts and avocets at Kesterson Reservoir.