Myth Power

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Raise your hand if you think DDT usage was the prime reason for the endangerment of the bald eagle population …

Yep, there are a lot of hands still up in the air despite facts that have proven this fallacy to the contrary.

News of the resurgence in Pennsylvania’s bald eagle population was recently reported, along with the continuing misconception regarding DDT.

Pennsylvania officials just announced success with their program to re-establish the state’s bald eagle population. But it’s a shame that such welcome news is being tainted by oft-repeated myths about the great bird’s near extinction.

In its July 4 article reporting that the number of bald eagle pairs in Pennsylvania had increased from 3 in 1983 to 100 for the first time in over a century, the Associated Press reached into its file of bald eagle folklore and reported, “DDT poisoned the birds, killing some adults and making the eggs of those that survived thin. The thin eggs dramatically reduced the chances of eaglets surviving to adulthood. DDT was banned in 1972. The next year, the Endangered Species Act passed and the bald eagles began their dramatic recovery.�

While the AP acknowledged the fact that bald eagle populations “were considered a nuisance and routinely shot by hunters, farmers and fishermen� – spurring a 1940 federal law protecting bald eagles – the AP underplayed the significance of hunting and human encroachment and erroneously blamed DDT for the eagles’ near demise.

How compelling is data against DDT being the primary agent in threatening the bald eagle population?

As early as 1921, the journal Ecology reported that bald eagles were threatened with extinction – 22 years before DDT production even began. According to a report in the National Museum Bulletin, the bald eagle reportedly had vanished from New England by 1937 – 10 years before widespread use of the pesticide.

But by 1960 – 20 years after the Bald Eagle Protection Act and at the peak of DDT use – the Audubon Society reported counting 25 percent more eagles than in its pre-1941 census. U.S. Forest Service studies reported an increase in nesting bald eagle productivity from 51 in 1964 to 107 in 1970, according to the 1970 Annual Report on Bald Eagle Status.

The U.S. Fish and Wildlife Service attributed bald eagle population reductions to a “widespread loss of suitable habitat,� but noted that “illegal shooting continues to be the leading cause of direct mortality in both adult and immature bald eagles,� according to a 1978 report in the Endangered Species Tech Bulletin.

A 1984 National Wildlife Federation publication listed hunting, power line electrocution, collisions in flight and poisoning from eating ducks containing lead shot as the leading causes of eagle deaths.

In addition to these reports, numerous scientific studies and experiments vindicate DDT.

U.S. Fish and Wildlife Service biologists fed large doses of DDT to captive bald eagles for 112 days and concluded that “DDT residues encountered by eagles in the environment would not adversely affect eagles or their eggs,� according to a 1966 report published in the “Transcripts of 31st North America Wildlife Conference.�

The USFWS examined every bald eagle found dead in the U.S. between 1961-1977 (266 birds) and reported no adverse effects caused by DDT or its residues.

Fairly compelling … but what about the theory of DDT causing thinning of egg shells?

One of the most notorious DDT “factoids� is that it thinned bird egg shells. But a 1970 study published in Pesticides Monitoring Journal reported that DDT residues in bird egg shells were not correlated with thinning. Numerous other feeding studies on caged birds indicate that DDT isn’t associated with egg shell thinning.

In the few studies claiming to implicate DDT as the cause of thinning, the birds were fed diets that were either low in calcium, included other known egg shell-thinning substances, or that contained levels of DDT far in excess of levels that would be found in the environment – and even then, the massive doses produced much less thinning than what had been found in egg shells in the wild.

So what causes thin bird egg shells? The potential culprits are many. Some that have been reported in the scientific literature include: oil; lead; mercury; stress from noise, fear, excitement or disease; age; bird size (larger birds produce thicker shells); dehydration; temperature; decreased light; human and predator intrusion; restraint and nutrient deficiencies.

So, the myths endure and respective interest groups are passionate to the degree where facts are not allowed to get in the way of the story.

A dangerous dynamic, fervor without all the facts …

I have to wonder …

Do “bumper sticker environmentalists” truly understand the damage that can be done when objectivity is foresaken and the cause is allowed to bury competing facts?

BTW … Yes, I did raise my hand to the question posed, so I’m red-faced, but thankfully at least more enlightened, as to the rest of the story regarding DDT and the power of a myth.

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