California condor egg shell thinning blamed on DDT — even though no significant correlation found

The AP reports:

In the coastal redwood forests of central California, scientists trying to unravel the mystery surrounding the reproductive problems of dozens of endangered condors think they have uncovered the culprit: the long-banned pesticide DDT.

The soaring scavengers with wingspans wider than NBA players are tall were reintroduced to the rugged coast of Big Sur in 1997 after a century-long absence. Upon arrival, the birds found plenty to eat, with dead California sea lions and other marine mammals littering the craggy shoreline.

While a good food source, sea lion blubber often has high levels of DDT, a pesticide banned in 1972 that has proven to be a persistent pollutant because it accumulates in bodies of creatures throughout the food chain when animals eat one another.

Once used widely in agriculture, DDT was banned because it is a human toxin considered a possible carcinogen by the U.S. Centers for Disease Control and Prevention.

Kelly Sorenson, executive director of Ventana Wildlife Society and a co-author of a new study on condors, said researchers who spent six years studying their reproductive problems have “established a strong link” to DDT in the birds’ food source…

Another former condor program manager, Noel Snyder, was critical of the DDT study, however.

He said it only looks closely at one potential cause of reproductive problems — DDT — and fails to properly evaluate the potential effects of other contaminants and factors that may be involved and more important.

“DDT is not the only thing that causes eggshell thinning, and the authors of the paper don’t present a significant correlation of DDT with the thinning found, and thus do not do a convincing job of linking DDT with the happenings in Big Sur.”

Read more…


  1. Why should they look any further when they have already found what they are looking for – a seed of hysteria they can plant and nurture into a full-grown research grant.

  2. Six years studying condor reproductive problems? Glad I got out of biology and into computers back in the 70s.

  3. Are they really trying to say that residual DDT, banned in 1972, is causing egg shell thinning? That’s not just a stretch, that’s a leap of faith.

  4. Yes, they are. You just don’t understand how those evil pesticides work.
    Natural solutions are so much better. Ever see those commercials for cactus juice and how wonderful it is? I was reading up on it:
    (Note: They are PROUD of this.)
    It seems enviros are proud of anything. This moth was possibly the only solution to Australia’s problem, but look at the lasting damage now rained down on other parts of the world. Nature is just as “evil” as any pesticide, but the greens never admit this.

  5. The other issue is that the Californian sea lion has an average lifespan of around 16 years. So where could the DDT actually be from?

  6. The DDT/sea lion blubber study is odd. It’s at

    There’s a known DDT hotspot in the ocean off of Palos Verdes, in Southern California. However, the levels in the sea lions were higher in Northern California … to me, that means the findings are suspect, although they try to handwave the problem away.

    The real killer issue is that the DDT concentrations have dropped by a full order of magnitude since 1970 … but in 1970 no problems were reported in vultures, which also eat dead sea lions, or in the sea lions themselves..

    Finally, there is no evidence presented of any correlation between shell thinning and sea lion DDT concentration … and absent that, the whole claim becomes unsubstantiated.


  7. Willis,

    If I remember correctly, the whole thinning eggshell study that spawned Silent Spring was not replicated. In my mind that leaves the DDT/eggshell link tenuous at best.


Your email address will not be published. Required fields are marked *