Wednesday, October 26, 2005

The last word?

More on the red chests of Pale Male's dynasty. I guess I'm convinced. And apologetic for saying that Blakeman's redtails lived in Illinois, not Ohio.


I'm in Ohio, two states further east than Illinois -- but that's really immaterial. (And I'm not sure where Queens or Staten Island are, either.)

I'm absolutely certain that the breast colors of the Central Park eyasses and immatures are not caused by anything they are fed or capture. The details supporting this contention are far too detailed to go into here, but they derive from both feeding trials of both American kestrels and red-tailed hawks that I conducted using a wide variety of foods.

But here, perhaps, is the clincher. If a particular Central Park prey animal causes the eyasses and first-year hawks to have pigmented breasts, why doesn't this persist through adulthood? The eyasses and first-summer birds are eating essentially the same prey as the adults. What would keep the accumulation of some prey-borne pigment from continuing to persist in new molted feathers each year? Lola appeared to have a rather typical white breast, and she was eating the same food that her eyasses were. She should have had a darker, pigmented breast, if food was the source of the pigmentation of the eyasses.

Savanna, my falconry red-tail, has a slightly darker, somewhat atypical breast coloration, approximating the beige or brownish hues of the Western race of the red-tail, Buteo jamaicensis calurus. I've worked with one of these dark-feathered birds trapped in the area 30 years ago, and two or three others have been seen. Many astute birdwatchers have noted these in Ohio, wondering if they are displaced, wondering Western birds. They are not. They are like the erythismal birds of Central Park, a local population with an atypical coloration gene. Western red-tails are noted for being smaller than our much larger Eastern birds. These dark Ohio birds have the bold shape and strength of our Eastern race, B. j. borealis. They are merely slightly darker forms of the local race, not wanderers in from the West.

All of this supports the notion that pigmentation in red-tails is entirely genetic, not dietary. The powerful protein-digesting enzymes of the red-tail's GI tract do a real number on flesh-borne pigments and most everything else, too (except fur and feathers, which get cast back out in the daily pellet). There is no way that food-borne chemical pigments can enter the hawk's circulatory system in a chemically undiminished form and then get chemically inserted in the new feathers being synthesized in the feather follicle.

It's a fun thought, however, and worthy of consideration. Good thinking by all.


John A. Blakeman