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Possible hybrid Harlan’s Red-tailed Hawk x Rough-legged Hawk in Kansas

Figure 1. Possible hybrid Harlan's x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Larry Hancock.
Figure 1. Possible hybrid Harlan's x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Larry Hancock.

In North America, Red-tailed and Rough-legged Hawks share highly variable plumages, often causing identification headaches for observers during migration and winter. It’s easy to chalk up a single odd trait to this variation, but what happens when a bird has several features that just don’t fit the mold for either species? Hybridization in raptors is generally rare, and it is especially rare among the familiar species of North American buteos. In late October, an interesting adult buteo was photographed in south-central Kansas that appears to be intermediate between a Harlan’s Red-tailed Hawk (Buteo jamaicensis harlani) and a Rough-legged Hawk (Buteo lagopus). Read on to learn more about this record, and to see more photos of this unusual bird.

Contributed by: Brian Sullivan (bls42@cornell.edu), Jerry Liguori, and Larry Hancock.

On 23 October 2011, Brian Sullivan and Larry Hancock were photographing Red-tailed Hawks on the prairie of north-central Oklahoma and south-central Kansas. They encountered an interesting buteo near the town of Caldwell, KS, which is the focus of this note. The bird was initially identified as an adult dark-morph Harlan’s Hawk in the field based on its dark overall coloration with whitish breast streaks. It is easily aged as an adult by its dark brown eye, well-defined dark trailing edge to the wing, and two generations of primaries. Harlan’s tail patterns are highly variable, but both observers noted a very unusual tail pattern for that subspecies, it being boldly and cleanly banded black-and-white, similar to an adult Red-shouldered Hawk but with more numerous, broader white bands. Upon review of photos, Jerry Liguori first suggested that this bird could be a hybrid between Harlan’s and Rough-legged. Several features of the bird support that identification, listed here in order of most to least significant.

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Figure 2. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Larry Hancock. Note feathered tarsi reaching down almost to the base of the toes.

Feathered tarsi—Red-tailed Hawks have bare tarsi, whereas Rough-legged Hawks have feathered legs down to the toes. The Kansas bird clearly has feathered tarsi that extend beyond what is typical of Red-tailed Hawk, but not reaching as far down the leg as would be typical of Rough-legged (Figs 1, 2). The leg feathering of Harlan’s is said to extend further down the tarsi than other forms of the Red-tailed Hawk (W.S. Clark, unpubl. data), but the extent of feathering on this bird reaches well beyond what is typical of that subspecies.

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Figure 3. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

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Figure 4. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

Underwing pattern—All light-morph Red-tailed Hawks have dark patagial marks, and these are even visible on most rufous-morph birds. Only on dark-morph individuals with completely blackish underwing coverts, are the darker patagial marks obscured. But on this bird, the patagial marks are the palest part of the mottled underwing, and the carpal area is darkest, suggesting the pattern of a Rough-legged Hawk (Figs 3, 5, 6). The dark carpal patches on all light-morph Rough-legged Hawks are even visible on many intermediate and dark-morph Rough-leggeds, with only the blackest individuals lacking such contrast.

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Figure 5. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

Tail pattern—Harlan’s Hawks have highly variable tail patterns, ranging from mostly reddish to grayish, whitish, blackish, and occasionally banded dark. Unlike other forms of Red-tailed Hawk, in most cases Harlan’s tails are distinctive in having some dusky mottling throughout, and in banded-tail types, the dark bands are often broad and frequently uneven and/or wavy or broken. The tail pattern of the Kansas bird is striking, especially dorsally (Figs 4, 9, 10). The evenly banded black-and-white pattern appears to be a cross between an adult male Rough-legged Hawk and an adult Harlan’s Hawk.

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Figure 6. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

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Figure 7. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

Flight feather pattern—Harlan’s Hawks’ flight feathers are highly variable, ranging from completely mottled grayish to evenly banded with black. Most often on banded-tailed type Harlan’s, the banding is thicker than is typical of other types of Red-tailed Hawks. Rough-leggeds have pale whitish flight feathers with faint, narrow banding. The Kansas bird has very fine banding on the overall pale flight feathers, which is more suggestive of Rough-legged than Harlan’s (Figs 3, 5, 6). Banding in the remiges is unlike most Harlan’s, which show thick bands that are often wavy or broken, and the black on the wing tips is often more prominent.

Structure—In the field the bird was distinctly Red-tailed Hawk-like in build. But when reviewing images of the bird’s structure (Figs 6-10) it shows some features that are more Rough-legged-like, especially the raised wrists with flattened hands resulting in a modified dihedral when soaring and gliding. Red-tailed Hawks typically have a more smoothly curved dihedral. While shape is hard to judge in photos, these may be at least suggestive of Rough-legged Hawk influence. The wing beats were stiff and choppy like Red-tailed Hawk, and differed from the more languid flap of Rough-legged Hawk. The Kansas bird appears to have a small head and bill more similar to Rough-legged Hawk than Red-tailed Hawk, but this is difficult to assess with certainty.

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Figure 8. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan. This shape is similar to a Rough-legged Hawk, with wings raised off the shoulder, and slightly flattened at the ‘hands’.

Body Plumage—The belly and chest have tawny-brownish tones throughout. Dark-morph Harlan’s show dark brown or blackish body plumage or dark brown bellies with rufous chests, but not tawny highlights throughout the underbody as on this bird. Several upperside traits fit better for Rough-legged Hawk than for Harlan’s Hawk such as the brownish-tawny upperwing coverts, slight grayish mottling on the back, and the grayish on the crown and cheek. These would all be unusual traits for dark-morph Harlan’s Hawk.

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Figure 9. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

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Figure 10. Possible hybrid Harlan’s x Rough-legged Hawk, Caldwell, KS, 24 October 2011. Photograph by Brian L. Sullivan.

Discussion

Hybrid buteos in North America are generally rare, but have been reported and confirmed on several occasions. Pairings have been noted between the following taxa: Red-tailed Hawk x Red-shouldered Hawk (photos), Red-tailed Hawk x Ferruginous Hawk (photos not available online), Red-tailed Hawk x Swainson’s Hawk, Swainson’s Hawk x Rough-legged Hawk (specimen and paper), Swainson’s Hawk x Red-backed Hawk, and possibly one other Harlan’s Red-tailed Hawk x Rough-legged Hawk in addition to our Kansas bird (that one photographed in California).
Harlan’s breeds throughout the farthest northwest reaches of boreal forest in Alaska and the Yukon Territory, and likely as far east as the Northwest Territories. Light-morphs have been documented breeding and as far south as the boreal/prairie interface in Alberta and once in North Dakota! Pairing with a Rough-legged Hawk seems logical for a vagrant Harlan’s that strayed far to the north outside the boreal forest and into the great treeless expanses inhabited by Rough-legged Hawks.