{"id":4139,"date":"2012-12-30T22:27:30","date_gmt":"2012-12-31T04:27:30","guid":{"rendered":"http:\/\/earbirding.com\/blog\/?p=4139"},"modified":"2012-12-30T22:57:53","modified_gmt":"2012-12-31T04:57:53","slug":"north-by-northwest","status":"publish","type":"post","link":"http:\/\/earbirding.com\/blog\/archives\/4139","title":{"rendered":"North by Northwest"},"content":{"rendered":"
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"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.<\/figcaption><\/figure>\n

There are few species in North America as ambiguous as Northwestern Crow (Corvus caurinus<\/em>).\u00a0 Even in a group of birds that are exceedingly similar the differences between American Crow (Corvus brachyrhynchos<\/em>)\u00a0and Northwestern Crow are minuscule at best.\u00a0 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).<\/p>\n

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.\u00a0 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.\u00a0 Outside of a narrow overlap zone in Washington state and southern British Colombia you can typically call the species by range alone.<\/p>\n

But the situation is more complex than just being able to tick a bird for your list based on where you are.\u00a0 The American Crows found along the Pacific coast (ssp. hesperis<\/em>) 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<\/em> 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).<\/p>\n

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 \u00a0sounded and looked more like “Northwestern” Crows in Washington and further north, and different from the American Crows further east.\u00a0 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.<\/p>\n

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.\u00a0 I also recorded some crows to the east of the Cascades, from the Okanogan Valley and further east.\u00a0 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.<\/p>\n

Unfortunately, as often happens with research of this type, what I found was different than either ideal situation.\u00a0 I’ve been able to hear what I feel are distinguishable differences between birds in Colorado and the ones in western Washington.\u00a0 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. \u00a0Recordings from further afield, in Oregon, California, and British Colombia seem to continue this cline. \u00a0On 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. \u00a0This would seem to show that the end of the cline in crow vocalizations is not where the species boundaries are currently drawn.<\/p>\n

When comparing the sounds from various crows it’s important to have an idea of what vocalizations each species makes. \u00a0Anyone 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. \u00a0The most common calls, though, are variations on the “caw” call. \u00a0These can typically be lumped into two groups, long and short, but there is a nearly complete continuum between those. \u00a0Often 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. \u00a0Here are two cuts from the same individual bird in Washington showing a long and a short “caw”.<\/p>\n\n\n\n
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