Hi all: I believe that field separation of Chihuahuan (CHRA) and Common (CORA) ravens is the most difficult ID problem in the ABA area of two undoubted species (Cordilleran and Pacific-slope flycatchers have had their separate-species status doubted frequently and fervently). Sure, some of the time that I spent in Colorado I was in a haze of thinking that it wasn't that difficult, but I had a string of sightings in the early 2000s that set me straight. I think that ravens with strongly wedge-shaped tails (that is, long and pointed; assessed on flying -- preferably soaring -- birds) are undoubtedly CORAs (probably males?), but nearly all else are very difficult, if not impossible, to assess certainly. The bill characters (bill longer with nasal bristles less than half the length of the bill for CORA; shorter and more than half for CHRA) are also good features, but these are typically difficult to assess with any confidence except at very close range (illustrated by Sibley). Sibley illustrates something that I've just noticed, so haven't had a chance to put to the test: he shows CHRA with four fingers when soaring, while on CORA he suggests a bit of a fifth finger. I'll leave that for resident CO birders to try out; here in Cape May, I don't get to see CORAs, much less CHRAs.
I am greatly uncertain of the efficacy of using the color of the down on ravens to ID them. I have seen wind-blow plumage of ravens with some frequency, but nowhere near often to have a good handle on how white is white. Oh, I have no doubt that it's a good in-hand character, but I don't know that it's useful as a field character. I have seen pictures of ravens with apparently very pale plumage showing in wind-blown sections of plumage, but with very long bills and relatively shorter nasal bristles. While, in general, CHRAs are more highly social than are CORAs, CORAs are certainly found in flocks, which are an aspect of age and mated status, not species. The younger and/or unmated CORAs hang out in flocks shortly after becoming independent of their parents, while mated birds are usually found in pairs and separate from other ravens (except when they have kids in tow). I don't know that CHRA pairs are as asocial as are CORA pairs, but in winter in the core of CHRA range, one generally does not find small numbers of CHRAs -- one finds lots or none. However, I have seen a single flock of >750 CORAs in the Sierra Nevadas, a place well away from any known CHRA range, and flocks of this size are, apparently, not abnormal for CORA, at least in places. To respond directly to Margie's query, social behavior is a valid ID character in some species -- e.g., American vs. Sprague's pipits -- but I don't know that it's all that useful in ravens. Range, as we know, is an excellent ID character, but one does have to fully understand the parameters of those ranges and any and all confounding aspects. In CO during raven nesting season (which at low elevation can be done by June!!), range is, in my opinion, one of the best ID characters to sort out the ravens. If one is on the plains at least 20 miles from a canyon or mountain, then there's a very strong chance that the raven one is ogling is a CHRA and if you're also south of the Palmer Divide, the usefulness climbs even higher. At all other seasons, range is, at best, a factor to consider, but certainly not one to pin one's ID on (except, perhaps, above Silverton in January; :-). Enjoy, Tony Leukering Villas, NJ -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
