(Nearly) Lost Wanderers

Early October, and soon we'll be seeing the last of these guys winging their way past the watch:

This is a Peregrine Falcon (Falco peregrinus). The name literally means wanderer, and it's appropriate. They live on every continent except Antarctica, and routinely show up in Hawaii.

There was a time, however, when this would have been an exceptional sight here in Illinois:

Starting after World War II, the US started using DDT to control mosquitoes and other insects. We used a lot of it, much of it for agricultural purposes. We didn't realize, though, that it bioaccumulates, (in other words, the higher trophic level you feed on, the more you absorb) especially in aquatic systems. Neither did we recognize that in larger doses it has serious impacts on calcium metabolism in birds.

Peregrines feed largely on ducks and shorebirds. (Well, today a lot of them feed on pigeons, but that's a rather new development.) That puts them squarely in a high trophic level, at the top of an aquatic system. So it's no surprise that they got doses more than high enough to disrupt calcium uptake. This is especially important for birds, since their eggshells are primarily made up of calcium. In the case of Peregrines, in the eastern US, eggs became so fragile that the females couldn't successfully incubate them. And by the early 1970's, Peregrines were no longer found east of the Mississippi.

After DDT was banned in the US in 1972, several of the most heavily impacted birds began to rebound. (Osprey, Bald Eagles, Brown Pelicans). But there weren't any Peregrines left to start a recovery. Into this gap stepped the folks at the Peregrine Fund. They raised a bunch of money, began to acquire Peregrines from elsewhere, and then learned how to successfully reintroduce them. As a result, they were removed from the US Endangered Species List in 1999.

But where did they come from? Therein lies an interesting debate on the nature of subspecies and the authenticity of our natural history.

The eastern anatum was gone -- there were a few pairs breeding in easternmost Canada that appeared to have been anatum, and that was it. Out west, they were still hanging on in scattered locations. So, what to do? Try to catch a few of the Canadian birds (which might have unfortunate effects on the one wild population left), or bring some western birds east?

Or you could try what the Peregrine Fund actually did -- bring in birds from all over the world, and rely on natural selection to sort out a new subspecies that would be well-suited to this new environment. (And a new environment it is -- many of the original nesting areas have become unsuitable, whereas many of today's birds nest in high-rise buildings in various cities.) These new birds are currently termed "mutts" by many raptor enthusiasts. I've been told that "nothing about Peregrine's nesting in Chicago is natural", to which I reply "What about Chicago IS natural?"

Admittedly, this is a long-term strategy. It will be decades, probably even centuries, before we can expect a population that is homogeneous enough to give it a subspecies designation all its own. But then again, that's how natural selection works.
One of the things that interests me about this is the insistence that the Canadian birds were still anatum, so they should have been used. Yes, they looked like birds from New York or Illinois, (or Florida, even), but does that mean that they would be genetically well-adapted to this area? That's an open question -- for most species, we don't have any idea how closely the genetics follow appearances across populations, and even if we did, we don't know which genes are important in adapting to local conditions. (Or even how closely those genes correlate with environmental variation.)

I do find the debate interesting, but fortunately for my own peace of mind, I find myself in agreement with the Peregrine Fund. This is a neat long-term experiment in applied evolutionary biology, and if we're still willing to do the work in the decades to come it could prove invaluable in helping us learn how species can adapt to the changes we like to make in our environment.

No matter how you feel about the current situation, though, it's neat to know that this shot could be across the sunrise of a new population, and not the sunset of a species: