North by Northwest

"Northwestern" Crow. This crow from La Push, Washington (on the outer Olympic coast) is supposedly a Northwestern Crow according to various sources. But is it really? Photo by Andrew Spencer.

There are few species in North America as ambiguous as Northwestern Crow (Corvus caurinus).  Even in a group of birds that are exceedingly similar the differences between American Crow (Corvus brachyrhynchos) and Northwestern Crow are minuscule at best.  The only “surefire” way to tell them apart is by range; however a number of sources also cite vocal differences as a distinguishing characteristic (e.g., the Sibley Guide, some versions of the National Geographic Guide, Birds of North America).

American Crow is a very familiar bird to most people in the US – it occurs throughout the lower 48, except for certain areas near the Mexican border.  Northwestern Crow is typically described as being found from northwestern-most Washington state along the Pacific coast to Alaska, as far west as Kodiak Island and the adjacent mainland.  Outside of a narrow overlap zone in Washington state and southern British Colombia you can typically call the species by range alone.

But the situation is more complex than just being able to tick a bird for your list based on where you are.  The American Crows found along the Pacific coast (ssp. hesperis) are at the small end of the spectrum for the species, sometimes look slightly “shinier”, and have subtly but noticeably different voices than American Crows further east (as an aside, the official designation of what constitutes hesperis is murky at best, and birds from as far away as Utah or Colorado could be this subspecies depending on some readings of the literature).

For a long time I’ve had a theory that the real “Northwestern” Crow was actually a “Pacific” Crow, since the American Crows along the northern California and Oregon coasts  sounded and looked more like “Northwestern” Crows in Washington and further north, and different from the American Crows further east.  If this was true, I theorized, then the crows west of the Cascades in the more humid areas of Washington, Oregon, and California, were a different species than those east of the Cascades in the drier rainshadow of the mountains.

So on a few recent trips I’ve taken to Washington I’ve made an effort to record crows wherever I found them, including going out to what were supposed to be the most “pure” Northwestern Crows left in the state, on the San Juan Islands and along the outer coast of the Olympic Peninsula.  I also recorded some crows to the east of the Cascades, from the Okanogan Valley and further east.  What I was hoping to find was either that the supposedly pure “Northwestern” Crows had a notably different voice than the taxonomically ambiguous ones around Seattle and along the outer coast in southern Washington, OR that all the crows west of the Cascades had similar voices that were different than crows to the east.

Unfortunately, as often happens with research of this type, what I found was different than either ideal situation.  I’ve been able to hear what I feel are distinguishable differences between birds in Colorado and the ones in western Washington.  But when I compared birds I recorded to the east of the Cascades in Washington I begin to hear what sounds like the start of a cline to the birds in Colorado.  Recordings from further afield, in Oregon, California, and British Colombia seem to continue this cline.  On the other side of the spectrum, though, when comparing the crows at the northwestern end of the range of American Crow to Northwestern Crows from Washington and further north into Alaska I don’t hear any vocal differences.  This would seem to show that the end of the cline in crow vocalizations is not where the species boundaries are currently drawn.

When comparing the sounds from various crows it’s important to have an idea of what vocalizations each species makes.  Anyone who has ever listened to a crow knows they have a remarkably large repertoire, everything from caws to screeches to rattles to song-like warbles.  The most common calls, though, are variations on the “caw” call.  These can typically be lumped into two groups, long and short, but there is a nearly complete continuum between those.  Often within any individual bird the long calls sound lower and more nasal, so care has to be taken when comparing different individual crows and making assumptions about differences in pitch.  Here are two cuts from the same individual bird in Washington showing a long and a short “caw”.

Ok so now to start the comparisons – listen here to what I consider a “typical” American Crow call from most of the continent, first longer calls then shorter:

And here is what I consider a typical American Crow from the Seattle area:

And a few from further east in Washington:

And here are some American Crows from further south along the Pacific coast:

Also listen to ML#13108 from the Willamette Valley of Oregon, ML#118854 from Tulare County, California, and ML#58191 from Hedley, British Colombia, all inland locations.

The ones around Seattle to my ears sound a bit more nasal, and on average slightly lower pitched than the birds from east of Washington state.  It isn’t a huge difference, and there is some overlap, but whenever I arrive in Seattle after spending time in Colorado or further east I hear the difference.  The birds from Okanogan County to the east of the Cascades sound similar to the Seattle birds to my ear, but are starting to having a hint of an eastern “accent”, as are the birds from coastal California. The recording from Oregon, though, sounds more eastern to my ears, and the ones from Tulare County, California, and British Colombia sound eastern to me.

Now listen to the calls of putative “Northwestern” Crows, also from Washington:

Not very different, right?  And here are links to some Northwestern Crows in the Macaulay Library from further north, far enough away from American Crow to be pure, supposedly: ML#132185, ML#136466, ML#58198.

Also not very different from the American Crows in Washington!

There are still some potential wrinkles to work out.  Without knowing the sex of the crow recorded it’s hard to determine what potential differences in male and female voices there are and how that affects the variation.  And it’s hard to get a real handle on the complete variation in each population without more recordings.

Now I can’t comment on the distinctiveness of Northwestern Crow based on genetics, structure or plumage, or physiological differences.  But I would contend that despite what many field guides, and BNA say, there are no compelling vocal differences between that species and American Crows in the Pacific Northwest.  With this lack of a vocal dividing line there seems to be little support for drawing the species boundaries in their current location.  Add to that the apparent evidence of a cline between the crows in the Pacific Northwest and those east of the mountains to the birds even further east, and the evidence for having two species at all starts to look weak indeed.

12 comments to North by Northwest

  • Ken Schneider

    Thanks for the very interesting information and discussion! Have you tried listening and comparing recordings while “blinded” to the location? With this sort of qualitative comparison, I would suspect that would be a valuable way of assessing whether there are real differences. You’ve gotten me interested in recording some of my local crows in central coastal California!

  • A great summary, thanks for sharing. Another potential confound in crow voices is age, as adults and immatures sound different in some ways that parallel differences between American and Northwestern Crows. For example, listen to the two crows in this recording, an adult and a juvenile:

    http://www.xeno-canto.org/72977

  • Alan Knue

    Michael Retter recently asked for my opinion on whether all crows along the Pacific coast between the Gulf of Alaska and southern California are the same taxon (including all “Northwestern” crows and “American” crows west of the Cascades and the Sierras) and that these crows are isolated by mountain ranges, appear smaller, and sound throatier (particularly from the Seattle area north).

    This was my response (edited) which is in accord with this great post:

    I actually don’t think there is a distinct taxon west of the mountains (at least in WA and OR). Remember, herperis (Western Crow) is a smaller, gruffer sounding bird. Johnston 1961 showed that crows pretty much in the range of herperis exist from Seattle south and from the mountains eastward. I just encountered American Crows in Yellowstone and Grand Tetons and they did seem a bit bigger than the Pacific NW birds, and definitely not as large as eastern crows. Vocally, they had some of that hoarseness you hear from the more coastal populations, but they definitely sounded different to those further west and further east as well. Eastern WA birds do not sound very different compared to those across the mountains and seem on the smaller side.

    I’ve read and heard that some Canadians still insist the crows in southern BC north along the coast and including Vancouver Is. are vocally, behaviorally, and ecologically distinct, but I’m unsure what they’re using for the comparison. From what I’ve observed in southern BC, I cannot find any evidence of 2 distinct populations and with no distinctions to go on, I how does one tell if there is anything different behaviorally or ecologically?

    I think all of the crows west of the plains are likely the same species with the birds north of Puget Sound smaller and perhaps more gruff sounding than other populations. Perhaps at one time they were isolated and on their way to becoming a separate taxon, but now there is no barrier and what we have is a cline in both size and vocalizations with small hoarse-sounding crows in Alaska when compared to crows from further south and east.

    Recent literature shows the following:

    Jønsson, Fabre, Irestedt. 2012. Brains, tools, innovation and biogeography in crows and ravens. BMC Evolutionary Biology 12:72

    They used nuclear genes from 1 individual each and there seemed to be about the same level of differentiation between caurinus and brachyrhychos as between the corone cornix and corone corone samples they used. The 2 specimens were both from the Burke Museum and I’m not sure where they were collected- so that in itself is interesting since if both birds were collected in the Seattle area, identified correctly, and showed this much difference in nDNA, then there really seem to be 2 taxon. They do not comment on this species pair in the text.

    Haring, Daubl, Pinsker, Kryukov and Gamauf. 2012. Genetic divergences and intraspecific variation in corvids of the genus Corvus (Aves: Passeriformes: Corvidae) – a first survey based on museum specimens. Journal of Zoological Systematics and Evolutionary Research Vol 50 Issue 3, 230-246

    They used mtDNA from 3 specimens of caurinus (2 from Seattle and another from Vancouver Island) and 6 of brachyrhynchos (2 MO, 2 KS, 1 ID, 1 unknown). They state “The second subclade of clade 6 consists of the Nearctic species C. caurinus and C. brachyrhynchos, which are not reciprocally monophyletic… C. caurinus and C. brachyrhynchos which are not differentiated in this mt sequence.” They go on to state “Hybridization between C. caurinus and C. brachyrhynchos has led to the discussions whether the former is merely a subspecies of the other. Land conversion by humans has facilitated the westward spread of C. brachyrhynchos and increased the incidence of the hybridization with C. caurinus to that point that today genetically distinct C. caurinus do not exist (Marzluff and Angell 2005). Although our sample size was small, our results support these reports.”

    They reference (which is on my list of things to read) Marzluff JM, Angell T (2005) In the Company of Crows and Ravens. Yale Univ Press, New Haven, CT.

    Since they used mitochondrial DNA, I’m not surprised by their results. The samples they used leave a lot of concern- they used no birds from Alaska and 2 of the NW Crows are from what many consider are minimally an intermediate population and very well could be ordinary American Crows!

    University of WA folks apparently have genetic data that supports separate species status, but I’ve heard varying reports of what that data is. And I don’t know where they think the boundary between the 2 occurs or whether is overlap.

    The crows that need more attention are those from peninsular FL- I read something recently (and can’t re-find the reference)that vocally these birds are closer to Palm Crows. True Florida Crow (pascuus) is also rather restricted in range and declining.

  • Janchris

    I live in Parkland,WA near Mcchord me like Shep Thorp consider’s most in the Puget Sound American/Northwestern Crow where the one’s east may have a small percentage of Northwestern cross they do totally sound different the the mid-west-east coast types I say has you get North of Everett,Olympic Pennsula, West Coast BC and Southern Coast AK are pure Northwestern Crows. On Stokes Field Guide it is said that American Crow ssp (Hargravei)are in South Idaho-Arizona-New Mexico. The true American Crow ssp (Brachyrhynchos)is around Northwest Territory of Canada-Texas-New Jersey and North. American Crow ssp (Pascuus)Cent.Fl and South. (Hesperis) ssp 3 different ranges Cent.BC-s Saskatchewan south to s.California; Colorado-w Kansas; LA-VA-n.Flordia.

  • Great post Andrew. What would be interesting is to hear recordings from birds in coastal SE Alaska (Northwestern Crow) and immediately adjacent Canada in the interior (American Crow).

  • P William Smith

    The issues you discuss derive not from biology, but from the frailty of human intellect. Linnaean taxonomy and nomenclature are artifiacts of the creationist mindset. Darwin showed that life is more complex. We as humans, however, cannot seem to get our minds around the full implications of evolution. We want the equivalent of a finite number of decimals in ? (pi). Well, we ain’t going to get it. We should all relax and quit trying to detect and count angels on pinheads. IMHO.

    P William Smith

  • Thanks for the great post Andrew. After looking at the sonograms and listening to this collection of vocalizations, I completely agree with your conclusion. I’m not hearing or seeing any real differences. I’ve always considered this species split to be a bit of a reach. When you talk to people who count Northwestern Crow, they are more inclined to talk about where they saw it rather than describe what they saw or heard.

  • George Armistead

    Alan Knue raises a most interesting point:
    “The crows that need more attention are those from peninsular FL- I read something recently (and can’t re-find the reference)that vocally these birds are closer to Palm Crows. True Florida Crow (pascuus) is also rather restricted in range and declining.”

    According to BNA, these Florida Crows have larger bills, noticeably larger feet, longer legs, seldom (ever?) flock, inhabit more rural areas (less suburban), and possess a greater vocal repertoire. While the Northwestern Crow has always enjoyed attention among us birders because the taxonomy is so vexed, as Alan suggests, we may be burying the lead.

  • Steven Mlodinow

    Thank You Andrew.
    The populations in w. Washington are not separated from those in e. Washington, and to my ear, the crows around Othello in Washington’s Columbia Basin sound more like the crows in Seattle than do the crows in coastal central/southern California. I’ve never liked the “Pacific Crow” theory. As for NW vs American Crow, that clinal change you describe matches well my experience. One of those weird questions that few seem brave enough to approach.

  • Ian Cruickshank

    On the north side of the border, to my ear at least, I have noticed interior British Columbia crows (adults) typically sounding slightly higher and less hoarse/nasal, compared to what I’m used to from living on the south coast of B.C. I’ve noted this in various locations from the Okanagan to Prince George to southeast B.C., in multiple years, and I doubt that this is just a bias resulting from my expectation of hearing a difference. Invariably, when I travel from the coast to the B.C. interior and listen to my first interior crow, I’m very soon struck by a bit of a different sound quality. A subtle, average difference, but more obvious than any differences I’ve struggled to hear between coastal southwest B.C. and Seattle. Crows in the prairie provinces and Ontario have struck me as clearly higher and less gruff/hoarse than coastal B.C. birds, perhaps more strikingly so than interior B.C. birds. Some anecdotal notes from one set of ears, anyways. Great post and great comments.

  • Michael Price

    In Vancouver BC, it’s sometimes possible, usually in winter, to hear a slightly larger crow uttering a higher-pitched yelp such as you typically hear in the background of movies shot in eastern Canada or US, which is very distinct to the west coast NW’ern’s deeper, harsher croak. Juv and 1st winter NW’erns can have higher-pitched calls than the adults, but these still differ in pitch and quality than possible brachyrhynchos. If you had to sound-bite it, caurinus croaks, brachyrhynchos yelps.

  • Jesse Ellis

    I’m up in the air on these birds, but I am wondering if a detailed analysis of the NW crows vs others would show more “roll” in their calls. There sounds to me (in your sample of 4) like a sort of pulsing quality that would be distinct from A. Crow if it’s really there.