Arsenic, mercury, selenium, and organochlorines and reproduction of interior least terns in the Northern Great Plains, 1992-1994

We evaluated concentrations of arsenic, mercury, and selenium in 104 eggs a nd chlorinated hydrocarbon compounds in 78 eggs of Interior Least terns (St erna antillarum athalassos) from Kansas, Nebraska, South Dakota, North Dako ta, and Montana from 1992 through 1994. We also reviewed data on Least Tern reproduction in the region. Arsenic was detected in only 13 eggs, and we d oubt that it affected the populations studied. The geometric mean mercury c oncentration for each state each year was below the level known to affect o ther avian species. Eighty percent of the eggs contained more than the thre e mu g g(-1) dry-weight selenium concentration considered unsafe for avian reproductive success. Concentrations of chlorinated hydrocarbons were too l ow to have affected nesting success. Nesting success reported for the study area was not sufficient to support the local populations. Nest flooding an d predation probably were the major causes of low recruitment, but determin ation of the effect level for selenium in Least tern eggs is needed.