Krider's is a Morph of Calurus?

posted by Jerry Liguori at
on Saturday, January 11, 2014 

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:

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.
 Adult Harlan's 
Adult Harlan's 
Adult Harlan's
Adult Harlan's
Juvenile Harlan's (left) Adult (right) - Same individual
Juvenile Krider's
  Adult Krider's
  Adult Krider's
  Adult Krider's
 Adult Krider's
Anonymous Derek Lyon said...

Very provocative title, got me quickly reading. I really like finding things out about raptor subspecies. Thanks Jerry! One quick question for you: in the 6th photo down from the top (Jim Lish's photo) it looks like a juvie Harlan's to me with the banded wing tips ... what makes this bird a Krider's?

And, from my reading of the Hull et. al. 2010 article I understood that Harlan's are as closely related to borealis as they are to calurus and that Harlan's is a subspecies of red-tail and not a distinct species on its own. I didn't get the impression of Harlan's being more closely related to borealis at all.

January 12, 2014 at 9:50 AM  
Blogger Jerry Liguori said...

Thank you for those comments Derek!

I read somewhere that the Hull paper said that but I'll check who quoted it. Either way, it confirms through DNA a subspecies. I guess the question is: is DNA enough on its own to merit that? It is a strong point, and I think the combined evidence suggests it anyway, but more study is being done, so we'll see. I'm always open to new stuff.

Krider's often have banded primary tips, a blog post for the near future, I mentioned it in a previous post (link below) but not on its own with photos. They are very similar sometimes, and thereasons for misidentifications in the past. Check out the thin bands on the tail and flight feathers, reddish hue to tail, faint patagials, and limited bellyband. The topside pic is best for ID, but didn't post it. Funny, my next post is on the tail patterns of juv Harlan's I'll post tomorrow.

January 12, 2014 at 10:03 AM  
Blogger Jerry Liguori said...

I re-read the paper, and I believe it suggests ithe DNA of Harlan's is more closely related to borealis than calurus? Maybe I am misinterpreting it....that is possible.

January 12, 2014 at 10:17 AM  
Anonymous Derek Lyon said...

I re-read the article too and I see your point now, I agree with you.

January 12, 2014 at 10:54 AM  
Anonymous Anonymous said...

I have Pyle's Identification guide but never read this section. I'll admit that after reading this and the previous post I wonder what else in there is wrong. I have a lot to learn about birds, so I don't want to learn poor information.

January 12, 2014 at 1:56 PM  
Anonymous Hatem Gomaa said...

You gotta admit, though, one of the more difficult things distinguishing between that light morph Harlan's and Krider's. The similarity is tremendous, including the mottling on some of the Krider's primaries, something one tends to associate strictly with Harlan's.

January 13, 2014 at 3:32 AM  
Blogger Jerry Liguori said...

Absolutely Hatem -- and it is the misidentifications that lead to bad data!

January 13, 2014 at 7:49 AM  
Anonymous Marc Grieco said...

I guess there's a reason I go to you with my hawk questions, thank you for sharing your knowledge on this blog it is a fantastic resource.

January 14, 2014 at 10:04 AM  
Blogger Jerry Liguori said...

Thanks for your trust Marc, and thanks for all the great questions you have sent me privately

January 14, 2014 at 10:06 AM  
Anonymous Seth Greenberg said...

I am not an expert on hawks but if Krider's is a calurus or both calurus and borealis, I quit!

January 15, 2014 at 9:58 AM  
Blogger Jerry Liguori said...

Hah Seth -- Don't worry, you don't have to quit birding or studying birds (if that's what you meant). Krider's is not a type of calurus.

January 15, 2014 at 9:59 AM  
Blogger Utahbooklover said...

I live on the west side of Brigham City and saw a white hawk that might be Krider's. Have you seen the white morph this far west? Any other white hawks that size in Utah?

January 16, 2014 at 11:10 AM  
Blogger Jerry Liguori said...

Hi Utahbooklover - There are lots of Harlan's around in winter, so I would think it was a light-morph Harlan's or maybe a leucistic Red-tail, but without a photo I couldn't say with certainty of course.

January 16, 2014 at 12:14 PM  
Anonymous Matt Finch said...

Utahbooklover, there's a leucistic redtail that migrates every year along that mountain from logan down. that might be the same hawk. I got reports from falconers every year that there's a "white redtailed" along that range.Try to get some photos of it! It seems pretty tame from what I hear.

January 17, 2014 at 9:09 AM  
Blogger Jerry Liguori said...

Matt - I actually have pictures from Bountiful Peak of a leucistic Red-tail, must be the one since it matches the plumage of the other shots I've seen.

January 17, 2014 at 9:14 AM  
Anonymous Anonymous said...

How do you tell the difference between a kriders hawk and a Harlan's Hawk? I took some pics of a hawk I've never seen before which was white. Many are saying its a Harlan's Hawk, but others are saying kriders. I'm confused? Wanted to post a couple pics but see now where to share the pics of the bird i captured with my camera.

November 28, 2015 at 6:11 AM  
Blogger Jerry Liguori said...

I'm happy to look at the pics, feel free to send them to

November 28, 2015 at 7:05 AM  

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