Eagle recovery still on, since DDT halt

One-paragraph in a story in the Philadelphia Daily Inquirer with a lot of impact:

A record number of bald eagles soared past Hawk Mountain in Berks County this fall, continuing a comeback that began with the banning of DDT in 1972. Then, 18 eagles were counted during the typical migration. The count this fall: 230. – Don Sapatkin

Caption from PennLive.com blog: Visitors and staff gather on the South Lookout at Hawk Mountain Sanctuary, near Kempton, Berks County. (HAWK MOUNTAIN SANCTUARY PHOTO)

Caption from PennLive.com blog: Visitors and staff gather on the South Lookout at Hawk Mountain Sanctuary, near Kempton, Berks County. (HAWK MOUNTAIN SANCTUARY PHOTO) (Photo substituted here for previous photo noted below, which has gone missing in DatedLinksLand)

 South Lookout at Hawk Mountain, Pennsylvania

South Lookout at Hawk MountainThe view from a rocky ledge near the entrance at Hawk Mountain provides a spectacular view of the countryside and is a good vantage point for watching migrating raptors in the fall. This photo was taken the afternoon of 10-16-2006.  Public domain photo, via Answers.com.

The white area at upper center is the “River of Rocks”. According to http://www.hawkmountain.org, this formation is a mile-long boulder field, up to 40 feet deep, which was deposited 10,000-12,000 years ago (the end of the last Ice Age), when glaciers stopped 40-50 miles to the north of this location. Repeated freezing and thawing cracked boulders from the ridgetop that gradually slid to their current position.

2 Responses to Eagle recovery still on, since DDT halt

  1. Ed Darrell says:

    Yes, but it’s not a post hoc error. Don’t confuse a legitimate cause-and-effect sequence with post hoc error.

    You’re watching the ornithological journals, I presume, and you know that the DDT/DDE concentrations in eagles stopped rising shortly after the EPA’s order to stop spraying the stuff on crops. Eggshell thickness follows almost exactly the same curve. As DDE levels decrease in the tissues of the parents, eggshell thickness increases, and chick viability increases.

    Since the ban, research has firmly established that DDE in raptors causes eggshell thinning, AND research has demonstrated that another effect — probably estrogen poisoning, but some sort of endocrine disruption — caused the chicks to be less viable, frequently dying in the egg regardless the breakdown of the shell, or dying within a few days after hatching.

    The confirming research is solid.

    Yes, we know that because of the decrease in DDT, eggshells of raptors thickened, and chick viability rose. No, it is not an error of logic to conclude that, especially when it is corroborated by at least two other independent lines of research.

    Sometimes, there really is a cause-effect relationship, no matter what fancy Latin phrase might be applied to the situation.


  2. HannahJ says:

    Post hoc ergo propter hoc.


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