Wednesday, May 31, 2006

It may not be the genes, says Blakeman

Trump-Parc nestlings getting ready to fledge
Photo by Lincoln Karim - 7/05


Here's a rather disruptive -- but very plausible -- thought that came to mind as I further pondered the orange-breasted eyasses so frequently seen in urban areas in the East since Pale Male began his wonderful reign. There is the possibility that the orange or buff bright breast color of city eyasses might be an artifact of the peculiar food big city red-tails are now feeding their young. It may not be genetic at all.

We know that the yellowness of the skin of raptors derives from carotenoid chemicals in their food. Captive raptors seen at zoos commonly have rather dull skin coloration, compared to the bright yellow of wild raptors feeding on wild prey. My falconry red-tail "Savanna II" does not have the bright yellow feet and cere found on wild red-tails. She doesn't eat a diet of primarily wild-caught food. Could the orange breast color of eyasses be caused by some pigment or basal chemical found primarily in city pigeons or rats?

Rural red-tails almost never capture and consume pigeons, and Norway rats, too, are infrequently captured. These two species comprise the vast majority of the meals for the Central Park and other urban-nesting red-tails in New York City. You mentioned an orange-breasted red-tail eyass in the Boston area. We mustn't arbitrarily assign this trait to a pigmentation gene descended from Pale Male or any of his kindred. This feather color may be a result of the unique prey city hawks are capturing and feeding to their eyasses. If so, there may be far greater genetic diversity in the NYC red-tails -- and that would be better (no inbreeding problems in the future).

The red-tails seen in Central Park in recent years may not have descended from Pale Male at all. The unique breast color of the urban eyasses may just be a particular nutritional result of the city pigeons or rats they are fed. That would explain the infrequency (absence?) of orange breasted red-tails in wilder, rural populations. And it might also dethrone Pale Male as the putative patriarch of all of the current orange-breasted urban eyasses hither and yon. I do think, however, that the paleness of Pale Male's head is purely genetic. I've seen an exact match to Pale Male sitting on a fence post a mile from my rural home here in northern Ohio. Both of these birds have been eating very different prey. My rural pale male has been eating lots of voles. Pale Male has been eating rats and pigeons, so the color of the head feathers of these two birds does not result from their food.

--John Blakeman