Pollutant levels in the great skua Catharacta skua

The great skua combines the traits favouring accumulation of pollutants. Levels of PCB and DDE are high, but there is no evidence of egg-shell thinning. There are indications of age-accumulation of heavy metals in adult great skuas and renal cadmium levels are very high in some individuals. Selenium concentrations correlate with mercury and cadmium concentrations. Possible protective effects of selenium are discussed. Levels of PCBs, DDE, HCB and dieldrin in eggs all correlate with each other, and vary greatly between individuals, suggesting individual variation in excretory rates, feeding habits or distribution in winter. Mercury levels in primary feathers correlate with those in liver so may be used to monitor without killing birds. The feeding habits and migrations of the great skua make it a suitable indicator of offshore pollution in the north-east Atlantic.