HATCHING FAILURE IN COMMON TERNS (STERNA-HIRUNDO) IN RELATION TO ENVIRONMENTAL CHEMICALS

The hatching success of two Common Tern colonies, a highly contaminated one at the Elbe estuary (Hullen) and a less contaminated one at the Jade (Augustgroden, southern North Sea coast, Germany), was similar in 1988; 69% at Hullen and 73% at Augustgroden. Most egg loss was due to predators. The number of eggs failing to hatch from unknown causes was 6-3% higher at Hullen than at Augustgroden. Egg-shell thickness and strength were not correlated with the chemicals' concentrations. At Hullen unhatched eggs were compared with randomly collected fresh eggs; the former containing a significantly higher amount (20%) of PCBs (134 mug) than the eggs collected at random (112 mug). Seven out of 45 PCB-congeners were found in significantly higher amounts in the failed eggs, among them the toxic congener PCB 138. The two samples showed no difference in mercury concentration, which was 6-2 mg kg-1, nor difference in shell strength. Eggs of Common Terns breeding at the Elbe estuary had concentrations of some contaminants reaching levels endangering breeding success.