While reading a column on Townhall I was struck by the absolutely bizarre numbers offered for eagle populations. From 500 breeding pairs in 1964 they now number 10,000 breeding pairs. In exactly 40 years their population has increased twentyfold?As they produce 1 to 3 eggs per year, that seems an absolutely impossible increase in population. It would require absolutely no infant mortality along with incredibly long lifespans and breeding cycles. Rats and mice manage such feats, but with long breeding cycles and small numbers of offspring, eagles just don't do that, even with the most aggressive protection by the government.

So, what happened?

Well, first, let us establish what did NOT happen. Banning DDT did nothing to help this population. As tests performed on quail and other birds show, the initial assumption that DDT caused shell thinning is simply not true. All of the shell thinning reported was better explained by climate variations, and a few other minor factors. Likewise, the populations supposedly in steady decline during the DDT years, such as peregrine falcons, were actually fluctuating, but relatively stable in numbers. So, let us immediately dismiss the idea that somehow banning DDT made the eagles increase in numbers.

It is possible the endangered species protection helped, though it is hard to see how it could account for a forty-fold increase in population over that short a period. Especially as the one group engaged in captive breeding was also the group granted waivers to ceremonially kill the eagles as well, making the breeding program relatively useless for increasing populations.

Two other articles give some clue about what happened.

The first article** gives numbers for two slightly different dates. According to this article, the population in the lower 48 states in 1963 was 417 breeding pairs. It also states that between the early 1970's when the animal was put on the endangered species list and the mid 1990's its population expanded fourfold. As it is doubtful the population increased much from 1963 to 1973***, then it seems safe to assume the population was maybe 500 breeding pairs when it went on the endangered species list. Which means there were 2000 breeding pairs in 1995.

The article also mentions that Alaska's population was 50,000 to 70,000 eagles in the 1970's and was not endangered.

The difficulty is fitting these numbers with the others. A fourfold increase, from 500 to 2000 pairs, in twenty years is plausible. But we are then left with a twelve year span , 1995 to 2007, during which there was an additional fivefold increase. That seems exceptionally fast.

There is another problem in that several sources argue that eagles dislike civilization, and avoid built up areas. As with all predators, they also have exceptionally large hunting territories. Which is why the increase from 500 to 200 make sense, as they were simply taking up available space, while going from 2000 to 10000 seems rather fast, as it seems the available spaces would become occupied and the rate of expansion would slow dramatically, while the numbers show an increase from fourfold increase in 20 years to fivefold increase in 12 years. Things just don't work that way.

But Wikipedia actually offers an answer***. As the first article mentioned the 50-70 thousand eagles in Alaska in the 1970's, Wikipedia mentioned that populations in both Canada and Alaska were not only not endangered but flourishing****, with one Canadian province having a population as high as 30,000 birds in the 1980's.

And there is our answer. Just as the decline had nothing to do with DDT, the increase had nothing to do with banning DDT. And while the endangered species act probably kept the new populations from being thinned, it did not cause the population increase. No, the simple explanation is that the new population really had nothing to do with those 400 remaining breeding pairs, their contribution was marginal. The new eagles were simply the overflow from the thriving Alaskan and Canadian populations which spread out into the lower 48 states.

Though I doubt ti will ever be publicized as such. The eagle is too much of a success story for the endangered species act for it to ever be truly investigated. And so we will keep hearing the myth that the government made eagles flourish, with not a word said about the thriving populations to the north, whose expansion probably accounts for almost every eagle now alive in the US.

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* I would provide citations, but cannot find web copies of many article son which I base this. Dixie Lee Ray wrote a fair summary of these findings in here Trashing the Planet, but many of the primary sources can be found in Rational Readings on Environmental Concerns, which I have mentioned before. One day when I have a lot of free time I will see if I can find online sources for these or similar articles so I can provide links when writing on AGW, DDT and other related topics.

** This article gives much more credence to DDT than I do. So please do not think I endorse the arguments, I simply use it for the numbers of eagles.

*** I know I criticize wikipedia, but in this case the article is strongly pro-conservation, so if the statements still argue against the conservation position it seems safe to assume they are reliable.

**** It is hard to reconcile this statement with the DDT theory of bird population declines. DDT was use din Alaska as much as it was elsewhere, and in Canada as well, yet somehow it did not cause bird populations to decline there. It seems that if two populations are both exposed to DDT and only one declines, perhaps an answer other than DDT needs to be sought.

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POSTSCRIPT

I do have to say the increase in population is amazing. In my youth I barely ever saw an eagle outside of a zoo, yet I have now seen several nesting pairs in the past few years. Of course, I have seen a similar expansion of raptors in general. Ospreys, cormorants, peregrines, red tail and red shoulder hawks have all increased in numbers quite dramatically.

I still think protective laws have less to do with it than other factors, including a general public opposition to indiscriminately killing birds of prey. However, I can think of one significant factor no one has mentioned. As poultry farming has moved from the open air to intensive, indoor factory farming, the need to kill off raptors to protect flocks has decreased dramatically. Is it accidental that the growth of factory poultry farms has coincided with the resurgence of birds of prey? (I have yet to explain the increase of aquatic birds of prey, but I am looking at that as well.)