White-faced ibis DDE-related reproductive problems continue at Carson Lake, Nevada

Organochlorine, mercury, and selenium contamination was studied in White-faced Ibis (Plegadis chihi) nesting at Carson Lake, Nevada in 1985 and 1986. DDE was detected in 138 of 140 eggs sampled. Eggshell thickness was negatively correlated with residues of DDE. DDE residues in ibis eggs, unlike residues in most other wading bird eggs from the Great Basin have not declined during the last decade. At DDE levels in eggs above 4 ppm (wet weight), clutch size and productivity decreased, and the incidence of cracked eggs increased. Assuming that 4 ppm DOE is the critical residue level, 40% of the nesting population in 1985 and 1986 was adversely impacted by DDE, with a net loss of 20% of the population' s expected .production. Most eggs containing high levels (up to 29 ppm) also contained DDT, which implies the source was recently-used DDT. No evidence of breeding ground DDE-DDT contamination was found.