Tuesday, June 21, 2011

The bird that shouldn't be

Northwestern CrowIf there really is such a thing, you should be able to call these crows in Victoria, British Columbia, Northwestern Crows. 16 September 2007 by Greg Gillson.

 

Regular readers of this blog know that on occasion I like to discuss field identifiable forms, or subspecies, of our Pacific Northwest birds. Such forms look and sound different than the "same" species elsewhere, and might be raised to full species status in the future.

However, this time, I'd like to discuss a species that is in your field guide that probably should not be there.

No, I'm not talking about the Pacific-slope/Cordilleran Flycatcher mess, or the 10 types of Red Crossbills proposed by call. I'm going to discuss the elephant in the room--the bird problem no one wants to acknowledge--the supposed "Northwestern Crow."

The range of Northwestern Crow (Corvus caurinus) is usually defined as along the immediate coastline from SE Alaska through British Columbia. Then its range is less well-defined, but into the Puget Sound region and northwestern Olympic Peninsula of Washington. You may find reference of birds to Long Beach and Vancouver, Washington, and even along the Columbia River from Astoria to Portland in Oregon.

As far as identification, it is supposed to be smaller than American Crow (Corvus brachyrhynchos) with faster wing beats and a deeper, raspier voice.

But guess what? There are pockets of crows along the Oregon coast, and even along the northern California coast, that are smaller than their counterparts 20 miles inland, and some are within the measurement range of Northwestern Crows (Measurements of Possible Northwestern Crows from Oregon. 1989. Range D. Bayer. Oregon Birds 15(4):281). They have more rapid wing beats and deeper calls. Are these, then, Northwestern Crows? This question has been asked for decades, with the usually accepted answer being "no."

The question of the status of Northwestern Crow in Oregon is somewhat of a template for discussing whether Northwestern Crow exists at all.

Northwestern Crows have been reported in Oregon since the time of Lewis and Clark. But Gabrielson and Jewett in their 1940 book Birds of Oregon had this to say: "Lewis and Clark... found crows abundant on November 30, 1805, at the mouth of the Columbia and listed them as Northwestern Crows, but unless the distribution of the two species has radically changed since that time, the Western Crow... was the more abundant species." Gabrielson and Jewett considered only 4 of the numerous crow skins taken in Oregon prior to 1936, and labeled Northwestern Crow, to actually be that species.

Subsequent evaluation of crow specimens from Oregon found none that could be clearly assigned to Northwestern Crow, and many were definitely female and juvenile American Crows. The book, Birds of Oregon: a general reference (2003, page 620-621, Marshall, Hunter, Contreras, editors) summed it up: "Given the lack of reliable specimen evidence, it cannot be shown that the Northwestern Crow has ever occurred in Oregon."

A study by D. W. Johnston in 1961 (The biosystematics of American Crows) found that Northwestern and American Crows were very closely related and may be conspecific (the same species).

The National Geographic book, Complete Birds of North America (2006, Jonathan Alderfer, editor) has this to say about the ID of Northwestern Crow: "Unfortunately, [C. b.] hesperis [Western American Crow] found in the Pacific Northwest is identical." That's pretty damning. As is: "Field identification within the suspected range of overlap in WA is probably impossible."

Thus, it is apparently only range that separates American Crows and Northwestern Crows. If you are in SE Alaska or the coastal slope of British Columbia and Queen Charlotte and Vancouver Islands, the crows are Northwestern. Inland in British Columbia and the rest of the West, including Oregon and California, they are American Crows. If you are in Puget Sound or on the Olympic Peninsula of Washington, well, then, I guess you can call them whatever you want.

That doesn't sound like a "good" species to me. Does it to you?

6 comments:

  1. Greg, Thanks for this very informative blog entry about "NW Crows"! Field guides and other guides don't cover this issue, so your blog helps!

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  2. The crows at Deception Pass State Park are noticeably small, but the ones living on my beach on Skagit Bay 2 miles away appear to be "full size." (He shrugs.)

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  3. Thank you for this post. I've been wondering about this distinction and identification since I moved back to the Northwest a few years ago.

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  4. What comments do you have on voice differences between American in coastal regions - from say Oregon - and those in the Okanagan. Is it safe to identify crows by call in the interior of Washington?

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  5. Or could it be an issue of interspecific competition with ravens? This is a biological principle observed among many species. If part of an animal's range overlaps with another similar species, then one of the two becomes relatively smaller or larger in the area of competition, to enhance its survival. The species as a whole does not change, and even in the affected area, you may find examples of a more normal size, hence, people reporting on seeing larger crows on the OP.

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  6. I believe there is a group (4 to 8) of American Crows near my house on 201st Lane on the Long Beach Peninsula in Washington. A block away, where the road ends and the beach path begins, there is another smaller group of distinctly different crows. I believe they are Northwestern Crows. I thought they were young ravens at first because their beaks are thicker, their eyes are larger and paler, their legs are longer and thicker, their chests seem broader. But now, at the end of August, the American crows seem to be gaining in size.

    I have photos of both group individuals and videos on YouTube under Sarah Sloane. I called the Northwestern candidates ravens. If anyone is interested in seeing the photos or hearing more about differences and similarities of behavior, I'd be interested in corresponding.

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