CLARIFICATION OF EFFECTS OF DDE ON SHELL THICKNESS, SIZE, MASS, AND SHAPE OF AVIAN EGGS

Moriarty et al. (1986) used field data to conclude that DDE decreased the size or altered the shape of avian eggs; therefore, they postulate d that decreased eggshell thickness was a secondary effect because, as a general rule, thickness and egg size are positively correlated. To further test this relationship, the present authors analysed data from eggs of captive American kestrels. Falco sparverius given DDT- or DDE -contaminated or clean diets and from wild brown pelicans Pelecanus oc cidentalis collected both before (pre-1946) and after (post-1945) DDT was introduced into the environment. Pertinent data from other field a nd laboratory studies were also summarized. DDE was not related to and did not affect size, mass, or shape of eggs of the brown pelican or A merican kestrel; but the relationship of DDE to eggshell thinning held true, Size and shape bf eggs of brown pelicans from the post-1945 era and those of kestrels, on DDT-contaminated diets showed some signific ant, but inconsistent, changes compared to brown pelican data from the pre-1946 era or kestrels on clean diets, In contrast, nearly all samp les of eggs of experimental kestrels given DDT-contaminated diets and those of wild brown pelicans from the post-1945 era exhibited signific ant eggshell thinning, Pertinent experimental studies with other sensi tive avian species indicated no effects of DDE on the size or shape of eggs, even though the high dietary concentrations caused extreme eggs hell thinning and mortality of some adult mallards (Anas platyrhynchos ) in one study. These findings essentially controvert the argument tha t decreased eggshell thickness is a secondary effect resulting from th e primary effect of DDE-induced changes in the size or shape of eggs.