The author is trying to pull just a wee bit of a fast one here by combining the affects of DDE and poor diet into an impact study of raptors. The fact is that no good studies have shown DDT to be a problem with raptors that had adequate nutrition, and raptors with poor diets have egg shell thinning problems regardless of DDT.
The real problem that falcons and eagles had in the US right up till the 1960's is that they were hunted nearly to extinction and their breeding and feeding grounds nearly eliminated. (Somewhere at home I have an article circa 1930 written by the head of the Ornithology dept at the American Museum of Natural History talking about how the perigine falcon was almost extinct and that this was a good thing). It was the change in protected status that lead to the comeback; banning DDT was coincidental but largely irrelevant.