" This was found to cause the link between the use by farmers of pesticides such as DDT and
dieldrin, and the decline of British populations of birds of prey."

If you do a lit search you can find a few hundred publications from the 60s and continuing thru the early or mid 80s on DDT concentrations in wild collected eggs.  These publications uniformly conclude that DDT either hurts hatchability or thins egg shells or both.  If you take a hard look at the actual data in these papers you rapidly realize something is wrong.  The data are wildly inconsistent even within one species sampled at two or more locations.  For example, the slope of the line plotting egg shell thinning versus concentration of DDT or a DDT metabolite changes by an order of magnitude with a change in author and location.  Some of this is without question due to poor analytical methods responding to components that have nothing to do with DDT which I already mentioned.

There without question was some man made chemical widely spread in our environment that was causing egg shell thinning in a great many species.  The range of species was far greater than simply raptors.  It also included most water fowl, particularly coastal ocean loving birds.  It was a world wide issue ranging from the arctic to southern S America.  It included both fish eaters and birds that did not consume fish as a primary diet.  To this day we do not know what the product was that caused this.  Perhaps PCBs?  They fit in many ways quite well, but no one has ever done testing to look for a link as far as I know.

Dick

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