|approximate stretch of road highlighted in pink|
|our position in FL as indicated by green marker|
This stretch of road cuts through agricultural land and is lined by tall powerlines that serve as perfect buteo perches. During more than two hours spent birding this road we had about fifteen RTHA sightings that, by photographic analysis, proved to be 11 different birds. They varied drastically in their plumage as you'll see below.
I'll start with the palest, most Krider's-like birds and move on from there. Several of these photos are quite poor and are meant for documentation purposes only, but I think they are still useful in illustrating the variation we encountered. As usual, click each image for a larger version.
|wish this one was in focus, would have been the best tail shot|
At one point this bird climbed into a soar and interacted with a darker bird (Bird #5) before returning to a telephone pole. The differences between the two birds are stark enough that I do not have to label which is which.
As for these pale birds, I'm not quite sure what to call them. If not Krider's, they can at least be called Krider's-like or possible Krider's intergrades. All three show at least some features associated with "Krider's" Red-tailed Hawks such as pale head, faintly marked underparts, white tail base, and pale upperwing mottling. But none are ghostly white birds like some of the adult male Krider's pictured in various guides and articles.
For an instructive read, check out this recent article on Krider's Red-tails by Jerry Liguori and Brian Sullivan.
[Note 2/8/13: Brian Sullivan was kind enough to review these images and confirm that these appear to be typical "Krider's" RTHA and are very similar to many birds he has seen breeding in the Dakotas. You will notice a similarity to birds photographed in the article linked above, and in the photographic supplement HERE.]
Whatever they are, they're beautiful. This part of Florida has a distinctly central/western avian feel to it; we had three Swainson's Hawks along this road, and there is a nearby small wintering population of Scissor-tailed Flycatchers and Western Kingbirds.
**The remaining eight birds are darker but show a great range of variation.
It would be instructive to find out where each of these birds breed. They all seem (to me) to be of the Eastern subspecies group, which to most authorities includes "Eastern" (borealis), "Krider's" (krideri, if it exists as a legitimate subspecies) and "Florida" (umbrinus). As noted above, the paler birds may be Krider's, and if so, they should have come from the northern Great Plains. As for the darker birds, I don't even have a good guess, though one would assume that during winter northern borealis augments, and likely outnumbers (?), the local umbrinus population in these parts. Variation within each subspecies gives me low confidence in identifying wintering individuals.
As always, comments are welcome.
Liguori, J. & B. Sullivan 2010. A study of Krider's Red-tailed Hawk. Birding 42(2):38-45.
Wheeler, B.K. 2003. Raptors of Eastern North America. Princeton University Press, Princeton.