Common vs. Chihuahuan Ravens

Common Raven, Bryce Canyon National Park, Utah. Photo by National Park Service (public domain).

Common Raven, Bryce Canyon National Park, Utah. Photo by National Park Service (public domain).

Every once in a while, somebody will put together a list of underappreciated identification challenges among North American birds.  Common and Chihuahuan Ravens always make the list.

Here in Colorado, we have lots of ravens. Conventional wisdom says the ones on the southeastern plains are Chihuahuans, and the rest are Commons. But not everyone accepts the conventional wisdom. Some believe that Chihuahuan Ravens are not only the default raven in the southeast, but also regular wanderers north to the Wyoming border.  Others maintain that to find a real Chihuahuan Raven, you have to go south of Colorado altogether.

For a long time, I haven’t been sure what to believe.  But I’ve been browsing my own audio collections and those online, and I’m starting to think that voice is actually a very good character — maybe the best field character — for separating these two species.  I’m willing to be convinced otherwise, and I’m interested in hearing from anybody who has experience with these two birds.  But at the moment, here’s what I think I know about the sounds.

Chihuahuan Raven

It seems to me that Chihuahuan Raven may actually have one of the most predictable (least variable) voices of any North American corvid.  Its classic call is a harsh “caw” that is deeper and much more coarsely burry than most “caws” of American Crow.  It is of medium pitch, slightly nasal, and barely upslurred.  It actually has something of a quacking quality — reminiscent of the harsh-sounding quacks that female Mallards do when they’re agitated.

Once you start comparing multiple recordings, this call of Chihuahuan Raven starts to seem remarkably consistent rangewide and from bird to bird:

Occasionally a couple of the birds in these recordings switch to some similar but slightly higher-pitched calls.  And females will also do the clucking gurgles that many female corvids do (you can hear some on my recording above from Chihuahua).  Other than that, though, these six examples are all so similar that they could almost be from the same individual bird.

Common Raven

From one of the least variable North American corvids, we transition to one of the most variable.

I’ve seen a number of sources argue that Chihuahuan Raven averages higher-pitched than Common Raven. This is a really problematic statement. It’s true that if you hear any really low croaks, you can be sure they’re from a Common:

But if you hear any really high croaks, you know they’re also from a Common:

(The ravens in that Red Top Ranch recording, by the way, were flying in a loose flock of 5 over featureless shortgrass prairie in southeast Colorado — location, habitat, and behavior all suggesting Chihuahuan Raven. But the voice doesn’t seem to match.)

Common Raven runs the gamut of possible pitches and tone qualities, from far below Chihuahuan’s pitch range to far above it. Chihuahuan occupies a limited space in the middle. Not only are Commons variable, but they often change sounds while you’re listening to them, unlike Chihuahuans. I might go so far as to say that if you hear a group of ravens giving a whole bunch of different-sounding calls, you’re almost certainly listening to Commons:

Some recordings of Common Raven come pretty close to matching the typical call of Chihuahuan Raven, but exact matches seem to be rare.  Interestingly, the most Chihuahuan-sounding Commons I’ve found are mostly from California:

You may recall that over a decade ago, Common Ravens in California were found to be genetically distinct from other Common Raven populations — more closely related to Chihuahuan Ravens than to other Commons. So should we split Common Raven?  Or reclassify California’s ravens as Chihuahuan?

Well, maybe not.  The study found that Chihuahuan Raven and “California” Common Raven were still pretty distinct genetically. And more recent followup research has showed that “northern” Common Ravens and “California” Common Ravens have apparently been interbreeding extensively in western North America for a very long time, and the genetic differences between them may be decreasing over time.  You could make a case for lumping ALL of North America’s ravens into one species, but I’m not sure that’s warranted, especially if Chihuahuans and Commons are not regularly interbreeding. More studies will need to be done on that.

On the whole, I could be underestimating the vocal variation in Chihuahuan Raven. And maybe there’s a lot of interbreeding going on in places like southeast Colorado. But at the moment, it really looks to me like Chihuahuan is a very predictable-sounding bird.  And if it is, then vocalizations may be the single best way to identify one in the field.

7 comments to Common vs. Chihuahuan Ravens

  • Mike Blair

    The Corvus genus in many parts of the world contains many populations whose identity and whose breeding distribution is similarly very difficult to define in any clear way. Australia is one example, although there they are steadily improving understanding of these circumstances, but across Central Asia and the eastern Palearctic, much needs to be done on vocalisations; the Chinese do seem to be tackling vocalisations generally. However, as far as I am aware, the only Corvus species complex undergoing extensive examination is C. macrorhyncus (Large-billed Jungle Crow). Since up to 7 species have been suggested, and over an enormous range, we may have to wait some time. Congratulations on making a worthwhile case!

  • Dan Lane

    So what is your take on the Colorado “Chihuahuan Ravens”? I don’t know their history, but (as I said in my comments to Andrew via X-c a while back), I have tried desperately to find the species there (from 2009-2013, at least), and despite seeing and hearing lots of ravens in the SE in proper Chihuahuan habitat, I have only been able to confirm Common.

  • Nathan Pieplow

    Well, I haven’t been to southeast Colorado since I gained my newfound understanding of raven ID. But now that you mention it, I am starting to be suspicious that Chihuahuan may be uncommon at best in Colorado. Back in the late 90′s when I was birding that area for the first time, looking for my lifer Chihuahuans, I didn’t find any really convincing birds until I got about 50 miles south into northeast New Mexico. In fact, I can’t actually recall any really convincing encounters of my own in Colorado since then. And I’ve seen/heard obvious Common Ravens nesting in the southeast in various places (including the John Martin Dam). So at the moment, you can count me as a Colorado Chihuahuan skeptic.

    (I should point out that there’s little argument that “real” Chihuahuans have been present in Colorado historically — I believe there are specimens from the state. But I’m not sure how many of the recent records are truly good.)

  • Derek Lyon

    In the spring of 2013 I was birding in southeast Colorado for the first time. I saw my lifer Chihuahuans then. Being from the east, I had prepared for the ID challenge (Common vs Chihuahuan) for years prior to the trip. I can say that there’s no doubt that Chihuahuans are there, but I only saw them one time, and I was surprised at how many Commons I did see. I was in the area only for 3 days, birding from dawn till dusk each day, but from my records I saw around 30 ravens. Only 5 of these I could confirm as Chihuahuans, all the rest were Commons. So, for me, they are there, just not nearly as common as ‘Common’s.

  • Dan Lane

    XC18832 is another cut that sounds remarkably like your California Commons, especially with that one lower vocalization thrown in at 0:08.

    I don’t doubt that Chihuahuans may occur (or may have at one time) in Colorado, but I suspect that many folks who report them from there may be doing so because they expect them to be there, as it has become the “birding wisdom”, not because they are actually seeing or hearing characters that rule out Common Raven there. But my own visits to SE Colorado have been about one day a year for four years, so my opinions are based on a very small sample size, and could be totally off…

  • Nathan Pieplow

    Yes, I have my doubts about the ID of XC18832. To clarify: California Common Ravens can sound all sorts of different ways, just like Common Ravens elsewhere. But when I went looking for the most Chihuahuan-like Commons on XC, they ended up being from California. Coincidence? Who knows?

    If XC18832 is in fact a Chihuahuan Raven, then it’s an example of Chihuahuan vocalizing with greater variety than in those in my first six examples above. Perhaps those “slam-dunk” recordings are the “low-hanging fruit” of raven ID. I’m not sure.

  • Nathan Pieplow

    I just checked Bailey & Niedrach, and they list a number of Chihuahuan Raven specimens from Colorado (interestingly, including 3 high-elevation specimens from the 19th century from Summit and Lake Counties). The species was abundant all throughout eastern Colorado during the buffalo slaughter decades of the late 19th century. However, Bailey and Niedrach (writing in the early 1960s) say that all recent reports have been in Lincoln, Kit Carson, Cheyenne, and Kiowa Counties. This area lies almost entirely north of the current mapped range of Chihuahuan Raven. They make no mention of either raven species in the southeast south of the Arkansas River. The first Colorado Breeding Bird Atlas found lots of “Chihuahuan” Ravens in the southeast, along with lots of Commons as far east as Cottonwood Canyon, but found no ravens whatsoever in Kit Carson or Cheyenne Counties, and ravens in only a single block each along the southern border of Lincoln and Kiowa Counties. So you can make of that information what you like. But it seems that Bailey and Niedrach considered Chihuahuan Raven a very uncommon and range-restricted species in eastern Colorado, and more recent accounts of its status and distribution seem to have shifted its range southward and expanded it.