Hatching failure in common terns (Sterna hirundo) in relation to environmental chemicals

Area of Science:

• Environmental Toxicology
• Avian Ecology
• Marine Biology

Background:

• Common Terns (seabirds) in the Elbe estuary show high contaminant levels.
• Assessing the impact of environmental contaminants on seabird breeding success is crucial for conservation.

Purpose of the Study:

• To compare hatching success and egg quality between a highly contaminated Common Tern colony (Elbe estuary) and a less contaminated one (Jade).
• To investigate the relationship between contaminant concentrations (PCBs, mercury) and egg parameters like shell thickness, strength, and hatching failure.

Main Methods:

• Comparative study of two Common Tern colonies with differing contamination levels.
• Analysis of unhatched and randomly collected eggs for Polychlorinated Biphenyls (PCBs) and mercury concentrations.
• Measurement of eggshell thickness and strength.

Main Results:

• Hatching success was similar (69% Hullen, 73% Augustgroden), with predation as the primary cause of egg loss.
• Unhatched eggs from the Elbe estuary colony had significantly higher PCB concentrations (20% more) than fresh eggs.
• Specific toxic PCB congeners, including PCB 138, were elevated in failed eggs; mercury levels and shell strength showed no differences between sites or egg types.

Conclusions:

• While overall hatching success was similar, elevated PCB levels in Elbe estuary Common Tern eggs indicate a potential risk to breeding success.
• Contaminant concentrations reached levels that may endanger future breeding outcomes for this population.
• Further monitoring of contaminants and their effects on Common Tern reproduction is warranted.