A Simple Method of Predicting DDE Contamination and Reproductive Success of Populations of DDE-Sensitive Species

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Abstract
A simple predictive model is presented which relates eggshell quality, as measured by Ratcliffe''s thickness index, to DDE content and reproductive success in the Merlin (Falco columbarius). The model accurately predicts the nesting success of populations from which thickness indices are determined for single eggs in a random sample for nests. It estimates the DDE content within 20% and provides an accurate measure of the relative degree of DDE contamination without the expense and specialized equipment necessary for organochlorine analyses. The model appears to be applicable to populations of at least 3 subspecies in widely separated locations, but only to those populations whose breeding success is influenced primarily by DDE contamination. For those influenced primarily by other factors, it provides an estimate of the maximum likely nest success. The simple methodology used could be applied to any species in which eggshell formation is sensitive to DDE and for which an adequate data base is available. The technique should prove valuable in the management and monitoring of endangered species or heavily contaminated population.

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