wrote:

I'll play. By what mechanism did DDT in the food chain kill birds?

The DDT causes the shells on the eggs to be thinner and they break
before the embryo develops into a chick.


I don't think so. This conclusion - eggshell thinning - was reached on the
basis of two articles in 1967 and 1968. Both researchers measured eggshells
collected currently with those collected before 1947. The researchers
concluded DDT & DDE were to blame and rejected other possibilities (food
supply, radioactivity, oil, lead, mercury, stress, temperature, etc.).

Many other researchers said "Hmm, let's see," and began experimentation.

See:
#39 Many experiments on caged-birds demonstrate that DDT and its metabolites
(DDD and DDE) do not cause serious egg shell thinning, even at levels many
hundreds of times greater than wild birds would ever accumulate.

#40 Experiments associating DDT with egg shell thinning involve doses much
higher than would ever be encountered in the wild.

#41 Laboratory egg shell thinning required massive doses of DDE far in
excess of anything expected in nature, and massive laboratory doses produce
much less thinning than is seen in many of the thin-shelled eggs collected
in the wild.

#42 Years of carefully controlled feeding experiments involving levels of
DDT as high as present in most wild birds resulted in no tremors, mortality,
thinning of egg shells nor reproductive interference.

#43 Egg shell thinning is not correlated with pesticide residues.

#44 Among brown pelican egg shells examined there was no correlation between
DDT residue and shell thickness.

#45 Egg shells of red-tailed hawks were reported to be six percent thicker
during years of heavy DDT usage than just before DDT use began. Golden eagle
egg shells were 5 percent thicker than those produced before DDT use.

http://www.junkscience.com/ddtfaq.html#ref6

The most widely-read web article is he
http://www.stanford.edu/group/stanfo...and_Birds.html

in which the eggshell-thinning claim is asserted without proof. You'll note
that the article was written by Paul Ehrlich, a 1980's prophet of doom who
wrote several books claiming a third to one-half of humanity would die of
starvation within a decade or two.*

In my community, Ehrlich is most famous for the 1980 "Simon-Ehrlich" wager
in which an economist, Julian Simon, called Ehrlich's bluff. Simon proposed
a wager. Ehrlich was to pick five commodities and Simon would wager that
each would be cheaper in ten years. Ehrlich agreed and chose copper,
chromium, nickle, tin, and tungsten.

Ehrlich lost and paid off in 1990.

Point is, if Ehrlich was wrong about mass starvation, commodity prices, and
other assorted prophecies, there's an excellent chance he was wrong about
eggshells.

---------
* Books by Paul Ehrlich

"The Population Bomb"
"The End of Affluence"
"The Race Bomb"
"The Population Explosion"
"One With Nineveh: Politics, Consumption, and the Human Future
"Healing the Planet: Strategies for Solving the Environmental Crisis"
"Betrayal of Science and Reason: How Anti-Environmental Rhetoric Threatens
Our Future"