Organochlorine residues, eggshell thickness, and reproductive success of snowy egrets nesting in Idaho

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During 1979, 19 Snowy Egret (Egretta thula) eggs were collected at two colonies in Idaho and analyzed for organochlorine residues. DDE was detected in all eggs, DDT in 63%, and DDD in 53%. Eggshell thickness was significantly and inversely correlated with concentrations of these pesticides, especially DDE. In the colonies studied, reproductive success was below the rate required to maintain current population levels. Females that laid eggs containing residues of DDE greater than 5 ppm had more eggs disappear or break, fewer eggs hatch, and significantly thinner eggshells than females less contaminated with DDE. DDE contamination appears to be the primary factor responsible for reproductive failures in Snowy Egrets nesting in Idaho. Circumstantial evidence suggests that Snowy Egrets are being exposed to high levels of DDE while they overwinter in Mexico.

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Reference Code: A84FIN01IDUS

Full Citation: Findholt, S. L. 1984. Organochlorine residues, eggshell thickness, and reproductive success of snowy egrets nesting in Idaho. Condor 86(2): 163-169.

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