Temporal trends in metal levels in eggs of the endangered roseate tern (Sterna dougallii) in New York.

Female birds sequester certain organic and inorganic compounds in their eggs which have been widely used as a bioindicator for examining the body burdens of contaminants and therefore the temporal and spatial trends of the contaminants in the environment. The same analyses can also reflect the status or vulnerability of the indicator species. Extensive bridge de-leading activities in the New York Bight (Cape May to Montauk) in the early 1990s coincided with a long-term study of the endangered roseate tern (Sterna dougallii) on Long Island, New York, affording the opportunity to test the utility of such fish-eating species as bioindicators of lead contamination, as well as the potential impact on the bird population itself. In this paper we test the null hypothesis that there were no temporal trends between 1989 and 1994 in metal levels in eggs of roseate terns nesting at Cedar Beach, Long Island, where the birds have been declining since the late 1980s. We report levels and trends for cadmium, chromium, manganese, mercury, and selenium as well as lead in abandoned eggs collected each year. There were significant interyear differences for all metals, with 1990 to 1992 generally having higher levels than 1989 and 1994. The yearly differences were particularly prominent for lead, where the 10-fold increase may have been partially due to the increased removal of leaded paint from bridges in the early 1990s, leading to increased lead in the aquatic environment. Cadmium and chromium are also released during de-leading. The causes for the higher levels in the other metals in the early 1990s are unclear. Metal levels in roseate tern eggs are several times higher than the median reported for most birds, and the possible impact on the population requires study.