Active birders throughout southern Canada and the northern states are likely going to come across heavily-marked light morph Red-tailed Hawks. Red-tailed Hawks in the east show a great deal of minor variation to their plumage, and at no time is this more appreciated/noticed than it is during the winter months. As winter sets hold and birding slows to a crawl, birders by in large tend to afford a little more time for study of perched raptors. When approaching the ID of “Northern” (abieticola) Red-tailed Hawks, it is important to consider the following:
– There is no clear, obvious, universally-recognizable “dividing line” between Eastern and Northern. In Ontario, one cannot simply travel to the edge of the boreal forest and see a heavily-marked bird on the boreal side of the road, and a lightly-marked bird on the Great Lakes/St. Lawrence side of the road. There is a gradual blending of the two. The middle ground overlap zone consists of an interesting mix of gray-area birds, with each birder choosing their own threshold for what is, and what is not, a Northern RT. It is a completely arbitrary assignment in the end. Since birders are relying on their own skill set and their knowledge derived from the knowledge of experts in the field, it is possible that a great deal of (minor) variance exists.
– I recommend approaching the ID of Northern RT’s the way that birders approach other species that showcase a great deal of clinal variation, such as Iceland Gull or Dark-eyed Junco. It’s OK to leave birds unassigned, especially while in the field. Posting photos to groups such as this one will either reinforce your decision or open your mind up to new approaches.
– A birder friend by the name of Brandon Holden uses the term “slider scale” whenever he refers to the Iceland-Thayer’s cline, and also the apparent kumlieni-glaucoides cline. I find this methodology helps me while I’m in the field and looking to assign Red-tailed Hawks to subspecies-level. Because these two subspecies (if that’s what “abieticola” turns out to be after actual study of its life history occurs on its breeding grounds) occur along a gradient, a slider-scale is effective in categorizing the two.
– Don’t get hung up on, to quote Cathy Sheeter, “soft” field marks such as throat markings, or legging markings, or various markings to the axillaries and so on. If you wish to get it right, get ready to be in it for the long haul, be open to receiving feedback and know that there are few, if any, certainties. Variation is the name of the game! To quote Matt Fraker, Red-tails are the Herring Gull of the hawk world. If one wishes to study Herring Gulls, especially in their immature plumages, one is genuinely in it for the long haul. Truly a lifelong study. If you rush and attempt to force field marks on birds in order to ease your approach (ease your aching mind) you’re likely to quickly dig a hole for yourself, and have missed most of the joy altogether…
– I should finish by saying that this is my fourth winter studying the Eastern/Northern Red-tailed cline. From 2013-2015, I learned an enormous deal of information from Jerry Liguori as well as Ron Pittaway and others. I am merely an enthusiastic conduit of their expertise on the subject. I do have what I believe are original working theories on the subject, but prefer not to (potentially) mislead the greater birding community by sharing them haphazardly. As ever, I am happy to receive materials such as photos, comments and findings by email at: firstname.lastname@example.org.
Photo: An example of the use of a “slider scale.” My subjective impression on the bird at left is that it sits at about a 5-5.5/10, with 1 being a faintly marked, blondish Eastern (borealis) and 10 being an extensively-marked Northern (abieticola). The bird at right fits the profile of a 8-9/10 bird, so is, therefore, a strong example of a Northern (abieticola). Photo credits: KitKat Jarjour and James Barber.