Northern Red-tailed Hawk (Buteo jamaicensis abieticola) as a Distinct Subspecies

Introduction and Background
One of the most complicated discussions in the world of Red-tailed Hawks is the validity of the Northern Red-tailed Hawk (Buteo jamaicensis abieticola). Ever since it was described over seventy years ago (Todd 1950), the Canadian Red-tailed population has been on a seesaw of being a separate distinct subspecies or a heavily marked type of the Eastern Red-tailed Hawk (B. j. borealis).

The subspecies was described in 1950 by W.E. Clyde Todd where he collected 10 abieticola and borealis specimens in Canada and noted how the northern populations was like borealis but "underparts more heavily streaked; throat and upper breast darker colored (more brownish, less rufescent); upperparts (including wings externally) darker colored (more blackish); and subterminal black band on tail averaging wider."

The American Ornithological Society declined the acknowledge of the subspecies in their last subspecies assessment in 1957 and ending the age of looking for geographical variation in field work. Thirty years later, Dickerman and Parkes (1987) published a more thorough paper on abieticola and supported Todd's hypothesis that indeed a northern population existed. It also explain explained how the northern populations differed from borealis and calurus. Dickerman and Parkes also stated that many "calurus" identified in eastern US were in fact abieticola. Field guides that list subspecies (Wheeler 2003, Pyle 2008, Stokes 2010) in the past have also failed to acknowledged a distinct population in Canada. At one point, abieticola was even considered an intergrade between borealis and calurus (Clark and Wheeler 1997, Wheeler 2004). For the space of sixty-three years, abieticola was just considered a more heavily-marked borealis and just that. In 2010, ebird finally recognized abieticola and added it as a taxon. Starting 2013 and still is today, Avibase has considered abieticola as a form of Western Red-tailed Hawk (B. j. calurus).

Light was finally shed on the abieticola case when Ligouri and Sullivan (2014) explored the topic and give a thorough discussion on the population. After spending some time explaining how abieticola differs from other subspecies. The reason the subspecies has gotten so much bad publicity in the past is due to the fact we know nothing about their nesting and to the extents of their breeding range so to assume that more heavily-marked individuals are from Canada is a narrow-minded hypothesis.

Wheeler (2018) goes in depth with the discussion claiming that abieticola was nothing more than a type of borealis due to lack of breeding data, borealis in the US showing just as heavily marked individuals in breeding season and Canadian intergradation between calurus and harlani has made heavily marked hawks more common in boreal forests.

Identification

Despite the information presented above, I will proceed to educate you in the identification of abieticola. The description I have provided is a direct quote from my other journal post "Identifying US and Canada Red-tailed Hawks" as it goes in depth what's expected in the subspecies or not.

Head: Dark head. Throat streaked, collared or dark. Darker cheek normal.

Upperparts: Light to moderate white mottling on the scapulars.

Underparts: Bellyband moderately to heavily-marked and always black or very brown black, with each streak resembling an arrow shape. Barring often occurs if the bellyband is moderate. Legs are often unbarred. Breast white but can often be tawny or rufous and these individuals often appear incredibly similar to heavily-marked rufous morph Westerns (calurus). Sides of the breast often have black "dribbling" marks.

Wings: Little to no rufous on lighter morphs, but often heavily rufous on rufous-breasted individuals. Patagials thin but darker than normal borealis. Well defined trailing edge. Underwing coverts are almost always whiter than breast with the exception being intergradation with calurus.

Tail: Similar to borealis except with a broader subterminal band and they are more likely to show partial or complete tail banding.

Morphs: Mostly light but rufous have occurred. Dark morphs are hypothesized.

Juvenile: Nearly identical to borealis but with more variance, including more heavily marked underparts.

Distrubition

It is believed that abieticola breeds across the boreal forest across Canada from Yukon to northeastern US. There is one confirmed sighting in California from raptor biologist and eBird admin Brian Sullivan who noted in his observation, "In all likelihood abieticola winters sparingly throughout the West, probably similar to harlani in this regard." Another abieticola was spotted by raptor biologist and colleague of Sullivan, Jerry Ligouri, in Utah.

Pit Falls in Wheeler's Work

I've had many hours of discussion with many raptor experts on the status of abieticola and I get very complex and differing statements. Several believe it's borealis due to inconsistency in diagnostic features, lack of breeding data and southern birds showing heavier bellybands. And it appears these experts are agreeing with Wheeler's statement "The 'Eastern' subspecies exhibits considerably more plumage variation than previously described or depicted in any publication." He goes on to further explain he figured this out by looking at museum specimens.

I believe this is the first pitfall in Wheeler's work is providing a modern example showing that borealis can indeed be more heavily-marked. He failed to provide photographic evidence pertaining to southern Red-tails exhibiting the heavy bellyband. In his final remarks on abieticola he does provide four photos from Canada that are Eastern-type hawks. I believe his purpose was to show that light-marked individuals can be found in northern Canada but it still doesn't answer my question, what about heavily-marked borealis?

I did find one iNaturalist sighting for a Tennessee Red-tailed Hawk in May. I have posted the observation link below. I can see how one might argue and claim this is a abieticola because of the black bellyband, dark throat and thick patagials. Not to mention it's breeding season and it's way out of its "breeding range". Despite the similarities this individual shares with northern populations, there's two solid features here that's telling me it's an abieticola. One, is that there is nearly no streaking on the sides of the breast and what there is, is not black as it should. Secondly, the subspecies is known to have broad subterminal bands despite the very thin one this individual is showing. So in a nutshell, I agree with Wheeler that borealis are indeed much more variable than previously believed but the features a heavily-marked individual has is still differing from northern populations. I will even mention, if this was an abieticola it doesn't mean it's not a nod to the subspecies being invalid. Let's remember in 2010, a Harlan's Hawk was found breeding with a Red-tailed in North Dakota when it's "breeding" range only a decade ago was only Alaska.

https://www.inaturalist.org/observations/25472293

I think the second mistake is claiming that northern Red-tails are exhibiting heavier bellyband due to intergradation with calurus. However, if that were true, why are we not seeing abieticola-like individuals in eastern Colorado. The Colorado Rocky Mountain front has been known for years as a heavy intergradation zone for calurus and borealis, yet we are not seeing these blobby bellyband individuals like in northern Canada.

Thirdly, if abieticola is not a subspecies, why are alascensis and furtesi still recognized? A group of birders called "Red-tailed Hawks of Western Canada" has admitted to the fact that alascensis is indistinguishable from calurus in the field because of the variance of the latter subspecies. As for fuertesi, I recently had a heated debate with another birder because I identified a Red-tailed as such in Oklahoma and the point of his argument was, how can we call it a possible fuertesi by a nearly nonexistent bellyband when some borealis in Ohio also exhibit no bellybands. Are we going to call them fuertesi too? As much as I hate to admit that (though the named subspecies has other differences from borealis), we can't ignore the fact that other subspecies are much more similar in appearance and yet none are reviewed for its validity.

Lastly, what about dark morphs? One of the reasons why calurus gets confirmed across eastern US is because they are the "only" subspecies with rufous or dark morphs. And it's easy to understand how one might show up in eastern US. The distribution of calurus is very similar to a Golden Eagle; summers/resident to western Canada, year-rounded resident to western US, winter visitor to Great Plains and annual or vagrant to eastern US. If you may see a Golden Eagle in Kentucky every winter, why not a calurus Red-tailed, a population with a very similar distribution.

However, there is a rising hypothesis that abieticola has dark morphs. This hypothesis started with Jean Iron (2012) who stated...

"When dark morph Red-tailed Hawks are seen in southern Ontario they are assumed to be from the western subspecies calurus. This is based on the belief that dark morphs do not occur in the Eastern Red-tailed Hawk borealis breeding population, whereas dark morphs occur in Western calurus. I wonder whether this assumption is always correct or if we should consider an eastern source for some of our dark morph Red-tailed Hawks.

The answer may lie in the northern Red-tailed Hawk population breeding in Canada’s boreal forest...I propose that a few dark morph Red-tailed Hawks probably occur in the abieticola population but have gone undetected in the vast boreal forest where few birders and ornithologists visit. This winter, 2011-2012, at least three and possibly four dark morph Red-tailed Hawks are overwintering near Toronto in Oakville, Oshawa, Guelph and Brantford. Some dark morphs may be breeding among the heavily pigmented abieticola population across the boreal forest. This makes more sense to me than thinking that all are western calurus."

Two years ago, eBird followed suite with the possibility that there are dark morph abieticola out there and proceeded in adding the slash calurus/abieticola. If you happen to be a user of eBird as well, if you see a dark morph Red-tailed Hawk east of the Rockies, it is best to use this slash instead of calurus/alascensis. I actually in fact used this slash a couple of days ago for a light morph Red-tailed (hard to believe) because it exhibited strong abieticola traits but the expected subspecies still couldn't be eliminated.

Conclusion

Though the subspecies may be thrown under the bus as a heavily-marked Eastern Red-tailed, abieticola still shows features that are inconsistent with even heavily marked southern Red-tailed populations. However, intergradation has probably interfered with them becoming such a clear-cut subspecies, especially if the intergradation zone between calurus and harlani extends from Gunsight Mountain, Alaska to North Dakota. There is also apparently problems identifying Red-tails in New England states as well as some Red-tails show very heavy brown bellybands and rich rufous breasts, suggesting a intergradation zone between borealis in that region.

As for it's validity as subspecies, I'm on the vote for yes it is. If it is true that abieticola can indeed have rufous or dark morphs, then it truly is a different subspecies from borealis. But we don't have that information yet. I see this decision of it's validity is very similar to the Harlan's Hawk being elevated to species status. Though it is behavioral and morphically different, we don't know how often it intergrades with other Red-tails and if they will willingly and consistent intergrade. It's just information we don't know yet and to make a decision on abieticola's status now appears premature and narrow-minded, especially in Wheeler's case as he failed to back up his statements with photographic evidence and/or data charts supporting his statements. As Jerry Ligouri stated...

"Although Northern Red-tailed Hawk is slowly becoming more familiar to raptor enthusiasts, much remains to be learned. With today’s advanced technologies for communication, documentation, and data archiving, birders can make solid contributions toward understanding this enigmatic bird’s identification, taxonomy, and natural history."

Acknowledgements

I would like to send some shout-outs to those who have helped me in my progression in understanding and identifying Red-tailed Hawks correctly. I would like to thank Jerry Ligouri and Brian Sullivan for spending some time with me, teaching me how to identify Red-tailed Hawks to subspecies level and how to identify abieticola. I thank Mike Borlé for taking his time in identifying several Red-tails I was skeptical about and trying to guess where the bird originated from. I also thank him for identifying my calurus/abieticola hawk. Shane Brown for sharing opinions on how "well-recognized" subspecies such as fuertesi or alascensis is not a valid subspecies. INaturalist psweet for recommending Wheeler's guide and giving me a new perspective on abieticola besides Ligouri and Sullivan's opinions on the matter. INaturalist Greg Lasley for tagging me in odd Red-tailed/Buteo observations and giving me a further appreciation for Red-tailed variation. INaturalist Bill Chambers for his comment, "when they come through you can really see the difference" when I identified one of his fall sightings an abieticola furthering my hunch that there's a distinct population up north.

Literature Source

- Dickerman, Robert W. and Kenneth C. Parkes 1987 -- Subspecies of Red-tailed Hawks in the Northeast (https://nybirds.org/KB_IssuesArchive/y1987v37n2.pdf)
- Dickerman, Robert W. 1989 -- Identification of Red-tailed Hawks Wintering Kansas
- Iron, Jean 2012 -- Dark Morph Red-tails: calurus or abieticola (http://www.jeaniron.ca/2012/darkredtailsTOCNews.pdf)
- Ligouri, Jerry 2001 -- Pitfalls of Classifying Light Morph Red-tailed Hawks to Subspecies
- Ligouri, Jerry and Brian Sullivan 2014 -- Northern Red-tailed Hawk (Buteo jamaicensis abieticola) Revisited (https://northernredtails.files.wordpress.com/2014/08/rth_aabieticiola_north_american_birds_march_2014.pdf)
- Ligouri, Jerry and Jon Ruddy 2014 -- Northern Red-tailed Hawks (https://northernredtails.wordpress.com/)
- Ridout, Ron 2014 -- Identifying Northern Red-tailed Hawks (https://ebird.org/canada/news/identifying-northern-red-tailed-hawks/)
- Jon Ruddy 2014 -- "Northern" Red-tailed Hawk (abieticola): Identification, Natural History, and Winter Survey (http://jonruddy.blogspot.com/2014/02/northern-red-tailed-hawk-identification.html)
- Todd, W.E. Clyde 1950 -- A Northern Race of Red-tailed Hawk (https://northernredtails.files.wordpress.com/2014/08/toddwec-1950-annals-31_289_297.pdf)
- Wheeler, Brian K. 2018 -- Birds of Prey of the East
- Wheeler, Brian K. 2018 -- Birds of Prey of the West

Posted by birdwhisperer birdwhisperer, December 03, 2019 17:56

Comments

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Great article! I appreciate your time on this. I'm finding a number of these abieticola birds in West Tennessee in the colder months. Many return to the same areas each winter much like the Harlan's, Krider's, and dark morph (calurus/abieticola) birds that return to this area do. I find that the Northern subspecies birds, much like most of the Harlan's subspecies birds, are normally extremely skittish and difficult to photograph. They will fly straight away, voicing their complaints by calling as they fly away! The influx of these different subspecies and morphs of Red-tails into our area each winter is one of the things that I look most forward to each winter!

Posted by greenesnake 9 days ago (Flag)

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