At DDE levels in eggs above 4 ppm, clucth size and productivity decreased, and the incidence of cracked eggs increased. Assuming that 4 ppm DDE 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. Selenium and mercury were both accumulated by ibis on the breeding grounds in Nevada, but egg concentrations did not reach a level where effect on productivity could be detected.
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DDE, selenium, mercury, and white-faced ibis reproduction at Carson Lake, Nevada