MERCURY IN FEATHERS OF LITTLE EGRET-EGRETTA GARZETTA AND NIGHT HERON NYCTICORAX-NYCTICORAX CHICKS AND IN THEIR PREY IN THE AXIOS DELTA, GREECE

Mercury concentrations were measured in feathers of little egret and n ight heron chicks and in their prey in the Aries Delta, Greece. Signif icantly higher concentrations occurred in night heron than in little e gret in 1993. In the night heron the mercury content of feathers was n egatively correlated to the size of chicks, possibly due to inhibition of growth. Mercury concentrations were higher than reported for heron feathers in seriously polluted sites in North America and Japan, but the toxic hazard is unclear. Diets differed considerably between the t wo species due to use of different foraging habitats and this seems re sponsible for different mercury contents of feathers. Mercury concentr ations in the pumpkinseed sunfish Lepomis gibbosus, goldfish Carrassiu s auratus, and in dragonfly Odonata larvae were the highest among the prey categories. Frogs and water beetles Dytiscidae had moderate conce ntrations whereas saltwater fish and terrestrial prey had very low mer cury concentrations. The implication is that the deltaic marshes are t he habitat most polluted with mercury. Night heron chick feathers, fre shwater fish and dragonfly larvae could be used to monitor mercury con tamination in this region, but use of bird feathers alone could give m isleading results if changes in diet occurred.