Overland Flights of Terns and Consequent High Exposure to Polychlorinated Biphenyls (PCBs) in Northwest France in the 1970S

Sandwich (Thalasseus sandvicensis), Common (Sterna hirundo), and Roseate Terns (S. dougallii) made overland flights from a breeding site in Brittany (northwest France) to forage in a semi-enclosed basin (Rade de Brest) ∼30 km away in 1976 and 1978. The foraging area was contaminated with polychlorinated biphenyls (PCBs) and high levels of PCBs were detected in several tern eggs. Levels of PCBs in tern eggs were sufficiently high to have caused adverse effects on reproduction. PCBs should be considered as potential contributory causes of declines in tern populations in the 1960s-1970s, in addition to other known causes including predation and trapping in the winter quarters.