Trace element and organochlorine concentrations in California clapper rail (Rallus longirostris obsoletus) eggs

Trace contaminant concentrations were measured in eggs of endangered California clapper rails (Rallus longirostris obsoletus) collected from San Francisco Bay during 1975, 1986, and 1987, and in clapper rail eggs (R. l. waynei) from North Carolina during 1987. Residues of 10 detected organochlorines (OC) were low and decreased by 2 to 3-fold from 1975 to 1986–1987 for San Francisco Bay samples, whereas eggshell thickness remained unchanged and comparable to eggs collected prior to 1940. Mercury (Hg) concentrations in eggs from San Francisco Bay were higher than those from North Carolina, and comparable to concentrations associated with reproductive effects in other avian species. Selenium (Se) concentrations in eggs from San Francisco Bay were also higher than those from North Carolina, and were highest in a north San Francisco Bay marsh adjacent to an oil refinery. Individual Se concentrations were slightly lower than values associated with embryotoxicity in other rallids. We recommend additional research on the effects of these and other contaminants on California clapper rails and the restoration of rail habitat.