Environmental regulators should consider screening chemicals notonly for cancer-causing potential but also for hormonal effects,according to a UC Davis scientist. Michael Fry, a research physiologist, has found evidence that seabirds, such as terns and gulls, are falling victim to estrogen-like chemicals introduced into the environment as common pesticides or industrial chemicals. For several years, Fry has observed that in areas of Southern California where the pesticide DDT still lingered in the environment, seagulls exhibited odd nesting behavior. Males lost interest in mating, an unusual number of females went to the breeding colonies and paired together in nests, and the birds' reproductive success was diminished. In the laboratory, Fry found that gulls injected with pesticides that mimic the female hormone estrogen produced male and female embryos with abnormal reproductive tracts. When mature, the offspring exhibited dysfunctional breeding behavior. "Birds and reptiles are particularly vulnerable to these pollutants because, unlike mammals, their embryos are in the closed environment of an egg, where the chemicals are simply recycled, rather than being excreted," says Fry. He will present his research findings Aug. 24 in Vienna during the International Ornithological Congress.