Utah Birders | Birding Blog, Utah Birds, Utah Birding, Utah Bird ID: Krider's is a Morph of Calurus?

Many birders and banders use the Pyle guide as a standard reference. While it is a great start for most species, there are some inaccuracies that birders and banders should be made aware of. I don't make a habit of pointing out errors in other's works, but I think it is helpful and appreciated. On page 445 of Pyle's guide it says: "Krider's Red-tailed Hawk…occur as vagrants to CA-AZ. These are medium to large in size…Krider's Red-tailed Hawk is here considered a white morph of borealis (Wheeler 2003), although, based on size it may also be a morph of calurus (Dickerman 1989), or of both subspecies." This sentence piques my curiosity. Before this quote, Pyle states the breeding range for Krider's pretty accurately as "south-central Alberta-eastern Manitoba to northern CO-northwest NB, winter to Texas." So how can Krider's be a morph of calurus, or, "a morph of both subspecies"? To clarify, in Wheeler 2003 it states that Krider's is a "pale morph" of borealis, and in the 1989 Dickerman paper, he does not associate Krider's with calurus. I'm also curious about what 'size' is being referred to here, and every Red-tail race is "medium to large" in size.

The issue with "Krider's occurring from California to Arizona" is that there are no substantiated Krider's records west of the Rocky Mountains. All of the reports in that area documented with a photo have turned out to be a light-morph Harlan's (the two subspecies can look very similar to each other). So, the Krider's referenced from CA-AZ is an extraordinary claim. Of course, Krider's could or has already occurred west of the Rockies, and I suspect it will be documented sooner or later for sure. Here are some Krider's and light-morph Harlan's below for future reference (check out the juvenile and its adult plumage a few years later -- follow-up instances like this are invaluable). And a downloadable PDF of a study of Krider's hawks. During this study, we did not see a single calurus from the grasslands of eastern MT to the MN state line south to SD, but did document many Krider's breeding with typical borealis and abieticola: http://www.aba.org/birding/v42n2p38.pdf

Just a side-note, the latin name is spelled "krideri" in Pyle's text, however, "kriderii" is the proper spelling, and describing Krider's as a "morph" is unusual since it has been proposed as a race in the past, may very well be today, and is typically treated as such in literature since it has a distinct breeding range, so defining it as a light-morph variant sounds better. To be fair, I know what it's like to have your ideas questioned. I stated about 7 or 8 years ago that I thought Harlan's Red-tail could be closely related to borealis for several reasons, and was dismissed by some. But recent DNA tests (Hull, et. al. 2010) show that Harlan's and borealis are closely related, and the two are found to freely interbreed. I can't fault anyone who makes mistakes researching the entire list of species and subspecies in North America, my point is to simply help rectify and decipher some issues.