Monday, May 4, 2009
Click the picture for a larger view.
Answer by Bryan Guarente and Tony Leukering
Bryan Guarente provided a good answer that is included, below.
"We are looking at a raptor. While we're down there, we might want to make note of the feathering that extends all the way down to the toes. This rules out all but three ABA-area raptors: Ferruginous and Rough-legged hawks and Golden Eagle.
"If you want to be really thorough, I guess you could look at the owls as well, but they are all ruled out by the plain dark underside combined with white undertail coverts, a combo of traits shown by no ABA-area owl. These features also make it easy to rule out two of the raptors mentioned earlier. White undertail coverts are shared by Ferruginous and Rough-legged Hawks (of the aforementioned three raptors), but Ferruginous Hawk lacks the dark belly in the light morph, as proven by the white undertail coverts. So, we are left only with Rough-legged Hawk."
It's tempting to try to age and sex the bird (remember, Rough-legged Hawk shows sexual plumage dimorphism), but the posture makes that task a wee bit difficult. The smooth dark of the left side of the belly patch suggests that our quiz bird is not an adult male, as they tend to have barred sides and little or no dark belly patch. Also, adult males tend to be grayish, rather than brownish, above.
Juvenile Rough-leggeds tend to have unmarked whitish heads, but I'm not absolutely convinced that we can see enough of the head to be sure of this feature on this bird, but the part that we can see is certainly well-marked, suggesting that it's an adult female. On the primaries that we can see on the left wing, the outer three (or so) are darker without the thin, pale tip of the browner, more worn feathers that are the next three (or so). This also suggests that the bird is an adult, as juveniles would have primaries all the same age and wear state. However, what we can see of the tail seems ambiguous to me, though leaning toward juvenile. This is because juveniles tend to have an ill-defined white-based, dark-tipped tail, while adult females typically show a well-defined dark subterminal tail band above the white tail tip and below the white tail base. Finally, the picture does not lie when it suggests that the photographer (me) was pretty close to the bird, another feature that suggests that it is a juvenile, as adults tend to be much more wary than this. I took the photo along US 36 in Washington Co., CO, on 26 December 2008 on my way to the Bonny Reservoir CBC that took place the next day.
Tallies of incorrect species provided in answers:
Red-tailed Hawk - 3
Swainson's Hawk - 1
The 25 of 29 providing the correct answer:
Answer: Rough-legged Hawk