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DDE-induced Eggshell Thinning in White-Faced Ibis Date Posted: January 22, 2003 A continuing problem in western United States: White-faced ibis (Plegadis chihi) nesting in Arizona in 2000 exhibited extreme eggshell thinning and possible reproductive failure associated with high egg residues of DDE, a break-down product of DDT. A small colony of approximately 75 pairs nested relatively late in the season and egg laying occurred from about June 15 to June 29. Average clutch size in 19 marked nests was 2.5 which was low compared to that reported for most other ibis populations. Thirteen of 30 eggs remaining in active nests hatched for a hatching success rate of 43%. DDE residue in eggs were similar to those reported in other ibis populations where DDE-induced shell thinning resulted in reproductive failure. Two of 16 eggs collected from marked nests were extremely thin-shelled as evidenced by a flexible shell that easily indented with slight finger pressure. Overall eggshell thickness of 23 eggs was 15% thinner than shells of museum eggs collected before the widespread use of DDT. Only 1 of 23 eggs contained mercury at potentially harmful concentrations. Selenium in 74% of the eggs was slightly elevated, but none exceeded levels known to be toxic.
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