Posted by Bob Lefebvre
Recently Terry Korolyk spotted an interesting hawk on Hwy 549 just west of Hwy 773, south of Calgary. Terry says it is an intergrade Harlan’s light phase Red-tailed Hawk.
Thought some Birds Calgary viewers might like to see what this bird looked like. The underparts are obviously a mix of both subspecies. The underside of the tail is obviously white with duskiness near the tip. The upperside of the tail was, in reality, white with a reddish subterminal band and 2 narrower wavy reddish bands adjacent to that.
Photographed by Terry Korolyk on April 6, 2012. Click to enlarge.
To fully appreciate the bird in the photo, look at images of adult Harlan’s Hawks and of adult Eastern Red-tails, then look at my bird again. Rather than blackish underparts with a white streaked throat like a Harlan’s Hawk, or, rather than having white underparts with a strongly streaked belly like an Eastern Red-tail, you have a bird with underparts markings that meet in between. The upperparts are clearly blackish like a Harlan’s Hawk, but they also have that Eastern Red-tail brownish cast. The tail was white like a Harlan’s Hawk, but, rather than having a dusky tip, it had 3 narrow wavy reddish lines there indicating normal light-phase Eastern Red-tail association.
As Terry says, the usual Red-tailed Hawks here are the Eastern subspecies, and “Harlan’s” Hawks are considered to be another subspecies of Red-tailed Hawk. At one time, Harlan’s Hawk was considered to be a separate species entirely. Intergrades like the one above indicate that they are varieties of one species (many people believe that Harlan’s is a separate species; perhaps genetic testing will settle this question).
The Harlan’s Hawk is very different from all other Red-tailed Hawk subspecies. In both its dark and light forms it has black and white plumage, lacking the reds and browns of other Red-tails. The tail, however, can have a wide variety of patterns. Harlan’s Hawk breeds in Alaska and northwestern Canada and winters on the southern great plains. We see them occasionally in Calgary in the winter months, when most other Red-tailed Hawks are absent.