Hi all: Ah, Bill Kosar posed an excellent question and Jeff Jones provided a bit of grist for the mill. Even though Bill's pictures were superb (unlike many of my photo quizzes), they would make excellent quiz photos, because ravens are probably one of the more intractable field-ID problems in North American birding. However, I believe that I can provide a definitive answer.
One of Jeff's points -- and it was a good one -- concerned wing:tail ratio. However, this ratio is dependent upon two variables, not just wing length. Additionally, both of those variables (wing, tail) are not independent, as they're also both related to overall size of the bird. Chihuahuan Raven (CHRA) is smaller than Common Raven (CORA); with experience, one might have gotten an indication from the bird's size relative to that of the post. Of course, as none of us saw the post in situ, we cannot use that hint, though I will say that the bird struck me as large when I first viewed the pictures. Back to wing:tail ratio -- CHRA may have relatively shorter wings than do CORA, but they have much shorter tails -- even relatively. Of course, tail length is variable in ravens and, I suspect, probably linked to sex (with males having longer, more wedge-shaped tails than do females), so if we could but know the sex of the bird.... Sibley shows CHRA with a small distance between wingtip and tail tip, with CORA having a longer distance. Granted, this will vary among individuals, but I think that the feature is, at least, suggestive, and points to the bird being a CORA. The date would also suggest CORA as the default raven species for the location, as most CHRAs depart the state for the winter. But, the best indicator of ID is the bill length:nasal-bristle length ratio. Bill's bird has an obviously long bill with the nasal bristles extending just barely more than half the length. On CHRA, these feathers usually extend well over half the length of the bill on a much shorter (and usually deeper, relative to length) bill. The combination of very long bill, shortish nasal bristles, very long tail, and seeming largeness indicates to me that the raven is a Common. Sincerely, Tony Leukering Villas, NJ "Jeff J Jones" <jjo...@jonestc.com> Dec 14 07:03PM -0700 HI Bill, So what have you been hearing about this bird? After doing more research, I am starting to think that the bluntness of the bill-tip may be a better clue (e.g. chihuanhuan) than the rictal bristles. I wondered, and could not find anything on the web to give me the answer, if where the wingtip falls on the tail might be an indicator. Chihuahuan's are supposed to have relatively shorter wings than Common's, therefore it might be reasonable to expect that the folded wings would fall shorter on the former. I have referenced BNA, and the standard field guides but no mention on whether this can be used as a clue. Just that the former's wings are shorter. And your photos show this detail quite well. As I mentioned in my previous email, since we don't have voice and it didn't kindly part its neck feathers for the photo; rictal bristles, bill tip and now possibly (if someone can offer some info on this) where the wingtips fall on the tail are what we have left. Anyone have any input on this aspect? Or - we can just ask Tony L. Jeff J Jones ( <mailto:jjo...@jonestc.com>; jjo...@jonestc.com) Teller County - 8500' - Montane Woodlands From: cobirds@googlegroups.com [mailto:cobi...@googlegroups.com] On Behalf Of BILL KOSAR Sent: Sunday, December 13, 2009 6:13 PM To: cobirds@googlegroups.com Subject: [cobirds] Common or Chihuahuan Raven? I have debated about this bird for a week. I saw it in an open prairie region east of Big Johnson reservoir in Colorado Springs. Please send me your opinion. http://avoapples.com/birds/IMG_7273_4x6.gif http://avoapples.com/birds/IMG_7269_4x6.gif Thanks Bill Kosar Colorado Springs bill_ko...@msn.com -- Colorado Field Ornithologists: http://www.cfo-link.org/ Colorado County Birding: http://www.coloradocountybirding.com/ You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.as/group/cobirds?hl=en
