numbe rs of fertile eggs. But few of the eggs hatched. ‘Many embryos appeared to develop
normally during the ea rly s tages of incubation, but died during the hatching pe riod,’ D r. DeWitt
s aid. Of thos e that did hatch, more than half died within 5 days. In other tes ts in which both
pheas ants and quail were the s ubjects , the adults produced no eggs whatever if they had been
fed ins ecticide-contaminated diets throughout the year. And at the University of California, Dr.
Robert Rudd and Dr. Richard Genelly re ported s imilar findings. When pheas ants received
dieldrin in their diets , ‘egg production was markedly lowere d and chick s urvival was poor.’
According to thes e authors , the delayed but lethal effect on the young birds follows from
storage of dieldrin in the yolk of the egg, from which it is gradually assimilated during
incubation and afte r hatching. This s ugges tion is s trongly s upporte d by recent s tudies by Dr.
Wallace and a graduate s tudent, Richard F. Bernard, who found high concentrations of DDT in
robi ns on the Michigan State Univers ity campus. They found the pois on in all of the testes of
male robins examined, in developing egg follicles, in the ovaries of females, in completed but
unlaid eggs , in the oviducts , in unhatche d eggs from des erted nes ts , in embryos within the eggs ,
and in a newly hatched, dead nes tling. Thes e important s tudies es tablis h the fact that the
insecticidal poison affects a generation once removed from initial contact with it. Storage of
pois on in the egg, in the yolk material that nouris hes the developing embry o, is a virtual death
warrant and explains why so many of DeWitt’s birds died in the egg or a few days after
hatching.
Laboratory application of these studies to eagles presents difficulties that are nearly
ins uperable, but field s tudies are now unde r way in Flori da, New Jersey, and elsewhere in the
hope of acquiring definite e vidence as to what has caus ed the appare nt s terility of much of the
eagle population. Meanwhile, the available circumstantial evidence points to ins ecticides. In
localities where fish are abundant they make up a large part of the eagle’s diet (about 65 per
cent in Alas ka; about 52 per cent in the Ches apeake Bay area). Almos t unques tionably the
eagles s o long s tudied by Mr. Broley were predominantly fish eaters. Since 1945 this particular
coastal area has been s ubjected to repeate d s prayings with DDT dissolved in fuel oil. The
principal target of the aerial spraying was the salt-mars h mos quito, which inhabits the ma rs hes
and coastal areas that are typical foraging areas for the eagles. Fishes and crabs were killed in
enormous numbe rs. Laboratory analys es of their tis s ues revealed high concentrations of DDT—
as much as 46 parts per million. Like the grebes of Clear Lake, which accumulated heavy
concentrations of ins ecticide res idues from eating the fis h of the lake, the eagles have almost
certainly been s toring up the DDT in the tiss ues of their bodies. And like the grebes , the
pheas ants , the quail, and the robins , they are les s and less able to produce young and to
pres erve the continuity of their race....
From all over the world come echoes of the peril that faces birds in our mode rn world. The
reports differ in detail, but always repeat the theme of death to wildlife in the wake of
pes ticides. Such are the s tories of hundreds of s mall birds and partridges dying in France after
vine s tumps were treated with an ars enic-containing he rbicide, or of pa rtri dge s hoots in
Belgium, once famous for the numbers of their birds , denuded of partridges after the s praying
of nearby farmlands. In England the major problem s eems to be a s pecialized one, linked with
the growing practice of treating seed with ins ecticides before s owing. Seed treatme nt is not a
wholly new thing, but in earlier years the chemicals principally used were fungicides. No effects
on bi rds s eem to have been noticed. T hen about 19 56 the re was a change to dual-purpos e
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