A Baffle of Crows

Northwestern Crow_DumasBaySanctuary-WA_LAH_9524r

Is that a Northwestern Crow or an American Crow?

Crows are one of the most common birds in the Pacific Northwest. There are crows in every tall fir, flying overhead, perching on lamp posts. You can’t miss them. And then, if you happen down to the beach—particularly in Puget Sound—there are hundreds more, picking through the seaweed on intertidal rocks, foraging through the debris left by the receding waters, feasting on dead sea life that has washed up on the sand. But, are those American Crows or Northwestern Crows?

American Crow_OceansideOR_20100204_LAH_8209The species have been considerate separate since 1958. Supposedly, Northwestern Crows are slightly smaller, and their voice is “huskier” (whatever that means). While American crows can be found across most of the US and Canada, Northwestern Crows restricted to a narrow strip of beaches and mudflats along the coasts of Washington, British Columbia, and southeastern Alaska.

If you’ve ever tried to distinguish between these two AOU species, you know how incredibly difficult it is. They’re both big, black birds. They both caw, at least to my ears. I’ve been totally baffled for years. The only reason I have both species checked off on my life list is because I’ve seen so many crows on the beaches in Washington that I have to assume some must be Northwestern.

Now, it appears that all that hemming and hawing and trying to decide if a caw was husky or not was a waste of effort. A recent study* of both species’ DNA reveals that they may actually be a single species.

Apparently, back in the ice ages, there were glaciers dividing two populations of American Crow. Those crows on the ocean side of the barrier diverged genetically from those on the inland side, and the one species began to become two.

Then the ice melted. With the barrier gone, the two groups of crows were once again able to interbreed. There were indeed two distinct populations—perhaps two distinct species—but the process of speciation has now reversed. In fact, there has been so much interbreeding that the paper’s authors doubt that any purebred crows remain. They’re all hybrids!

Northwestern Crow_FedWayWA_20090920_LAH_0851

The paper, by scientists from the University of Washington, the Burke Museum of Natural History and Culture, and the U.S. Geological Survey, was published in Molecular Ecology this week, so no action has yet been taken on the findings. Still, I wouldn’t be at all surprised to find that, when all is said and done, the two crow species end up lumped together. I’ll be sad to lose a lifer, but that loss will be more than offset by the relief that I no longer have to guess which crow I’m staring at!

* The actual paper is behind a paywall, so I was only able to read the abstract. There’s an easy-to-understand summary at Gizmodo.com.

The answer to last week’s quiz was a Hooded Merganser (female).

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