Sunday, May 24, 2009

On roughlegs

With the Rough-legged Hawk flight practically over, I realize that a blog entry on roughleg ID comes a bit late in the game, but hey - better late than never. Earlier in the season I didn't have all these photos yet.

Sunday's flight was unremarkable, so I'll just give you the numbers, and we can move on: 8 Turkey Vultures; 1 Osprey; 1 Bald Eagle; 4 Sharp-shinned Hawks; 1 Cooper's Hawk; 51 Broad-winged Hawks; 8 Red-tailed Hawks. That's right - zero Rough-legged Hawks! Somebody mentioned they saw one, but I didn't, and so... ha! doesn't get added to the count. That's how that works.

In North America, the Rough-legged Hawk breeds in the tundra and taiga of arctic and subarctic Alaska and Canada, and migrates across the boreal forest to winter in open country of southern Canada and northern United States (Bechard & Swem 2002). Whitefish Point is an important migration monitoring site for this species, and in fact holds the record for most roughlegs seen in a day (525 on April 23, 2000) and in a season (2,600 also in 2000) of all North American hawk migration count sites.

The Rough-leged Hawk shows a tremendous amount of variation in its plumages. Unlike other members of its genus (buteo), it even shows distinctive plumage differences based on sex, as well as age, and color morph. Let's review some of these plumages.

The bird shown at the top is probably the most characteristic plumage, with the bold carpal patches ('wrist patches'), the dark belly and the white tail with the broad dark terminal band. These are the field marks that most birders associate with this species. They are the field marks of an adult female.

The adult female is quite similar to the juvenile, but note on the adult female the darker markings on the underwing coverts (roughly the feathers between the belly and the carpal patch), and the dark trailing edge on the wing. The black terminal band on the tail is also more defined on the adult female, as compared to the juvenile.

Here is that juvenile. Note the unmarked underwing coverts, the absence of a dark trailing edge on the wings, and the less neatly defined tail band. That last field mark is harder to observe on a closed tail.

Now let's look at an adult male.

Compared to the female, we note that the carpal patches are less defined, that the belly only has some barring on the sides, not the solid black patch of the female or juvenile, and that the head is darker. The terminal band on the tail of males is well-defined but thinner, and often males show a few extra bands near the terminal band. On this bird, the two outer tail feathers appear to be free of extra banding, but a hint can be seen just above the terminal tail band in the middle. If this bird were to spread its tail, we would probably see one or more extra bands.

So much for the light morphs. This species also has a dark morph, and an intermediate morph. Dark morphs are rarer than light morphs, and intermediate morphs are rarer than dark morphs.

Here's an adult male dark morph.

It's a beautiful bird. Note the extra banding on the half-open tail. That, and the fact that the bird is pitch black, make it an adult male. Only the adult male dark morph is truly black.

Here's an adult dark morph that could be male or female. The dark trailing edge of the wings means that it's an adult, but in the dark morph roughleg, dark chocolate birds can be male or female. I'm inclined to say that's probably a female, given the tail pattern. It seems as if there is no additional tail banding besides that broad terminal band, but these things are hard to judge on closed tails.

Finally, a juvenile dark morph. There is no dark trailing edge to the wings, so it has to be a juvenile. The carpal patches and the dark belly are well defined.

This far I've only talked about plumage. On distant roughlegs, when plumage is not yet visible, a first clue will often be the way they hold their wings in a glide: the so-called modified dihedral, with wings raised but the outer parts of the wings held flat. They are a little bit longer winged than the Red-tailed Hawk, and from great distances can appear similar to Northern Harriers - especially males.

Literature cited:
Bechard, Marc J. and Theodor R. Swem. 2002. Rough-legged Hawk (Buteo lagopus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online:

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