OK, so I am going to get all technical on you today. Recently I heard a very informed person mention the Brown Pelican was not hurt by the chemical DDT which was banned back in the ’70’s. While this is technically true in that the birds themselves were not effected by the chemical in the environment, there was, it is thought, a significant impact on the population. I thought another person duped by clever manipulation of the facts. Rather than making the birds sick the chemical is thought to cause significant thinning of the egg shells (about 12%) of many bird species including the Brown Pelican. After a moment of satisfaction on my part, the informed person caught himself and stated just that, but then went on to say that even the thin shell theory is subject to debate. That led me think it may be true that the evil chemical DDT did not cause the thinning of the egg shells either. Let’ take a closer look.
On Nov. 17, 2009 the Department of the Interior removed the Brown Pelican from the Federal list of Endangered and Threatened Wildlife. The 29 page document goes into great detail about the measures taken to help the Brown, population changes, and even the impact of global climate change, but I did not find any reference to DDT or any other toxin once thought to be the primary cause of threatening the existence of the Pelican. During the time of protection many steps were taken to support the birds, creation of natural habitats, responsible management of oil spills were 2 large factors. Not only did the government take actions to stop the things leading to population decreases but created factors to increase populations. It worked. Still I thought it odd the main culprits not referenced in the document. A little more research uncovered some facts about DDT and the impact on egg shells.
First of all DDT actually has no effect on the eggshells is in fact thought to be a compound known as DDE (Dichlorodiphenyldichloroethylene) a by-product of DDT that is stored in the body fat of raptors and waterfowl. There is a measured correlation of DDE levels and shell thickness but also there is conflicting data. For example the Brown Pelican shells improved with the removal of DDT from the environment but after 40 years of the chemical being banned, California Condors still suffer from thin shells. It is thought that 6-10 years is required to flush traces thought the environment. It is even admitted the DDE damage is a hit and miss effect completely unchanging many bird species, in particular domestic breeds.
So yeah it is subject to debate, not only if it causes shell thinning but also how the DDE is introduced to the birds that are impacted.
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