Reproductive Outcomes in Colonial Fish-Eating Birds: a Biomarker for Developmental Toxicants in Great Lakes Food Chains II. Spatial Variation in the Occurrence and Prevalence of Bill Defects in Young Double-Crested Cormorants in the Great Lakes

The frequency of bill malformations in the double-crested cormorant chicks in the Great Lakes region was assessed from 1979 through 1987. Of the 31,168 chicks examined, 70 had bill defects, compared with two of 20,962 chicks examined in northwestern Canada. The likelihood of bill malformations in the Great Lakes ecosystem appears to be 20 to 30 times greater than in comparative ecosystems. This trend has been atrtributed to the presence of such toxic chemicals as PCBs.