Brian Sullivan and I just submitted an article to be printed in North American Birds on the "Northern" Red-tailed Hawk, referred to as B.j. abieticola, also referred to as "Canadian" Red-tailed Hawk. This is the heavily marked borealis type that often gets confused for Western Red-tailed Hawks reported in the eastern half of the U.S. in winter. Keep an eye out for these types….
What is abieticola? Well, Jon Ruddy from Ontario just did a piece on this taxon for eBird regarding the variants he sees in his neck of the woods, and it should be up on the site soon. Today, abieticola is thought of as a form of the Eastern Red-tailed Hawk (B.j. borealis), but not enough is known about it to say either way if it is a separate subspecies, as some have proposed in the past. It does inhabit a wide-ranging but specific area, and can be told from "southern" borealis (or what we think of as typical lightly marked borealis), but there is much overlap in the plumages of the two types, and they interbreed in southern Canada and the very northeastern half of the US. The purpose of our article is to bring some attention to the subject and get birders to document and take a second look at Red-tails in general. The article shows over 20 different individuals and gives a sense of the plumage variation within this type, so hope people see it.
Here are some "Northern" Red-tails, but the variation is extensive and shown in the print article: