Thursday, October 27, 2005

Blakeman on food and pigment

JB and Savannah

I should have mentioned that the soft parts of hawks are decidedly colored by their food. Feathers, no. But the intensity of the yellow of the feet and the cere, the soft band of skin around the bill, are markedly influenced by the hawk's food.
Birds of prey kept in captivity, either by falconers, zoos, nature centers, and the educational display birds of rehabilitators, seldom have the intense yellow exposed skin color of hawks that hunt exclusively in the wild. Wild food doesn't change the color from yellow. It merely intensifies it.
The color is probably caused by carotenoids, plant pigments that prey birds and mice have in their GI tracts from plant food they were digesting when caught. The intense yellow color on the soft parts of wild hawks is always impressive, compared to the unsaturated hints of yellow on our captive birds.
I didn't mean to imply that food provides no body pigmentation for hawks, only that food doesn't change feather colors.
Commercial pen-raised chickens are fed marigold extracts to give the fat and flesh a slightly yellow color. Without these food amendments, pen-raised chicken flesh would appear bleached. The color intensity of the flesh and eggs of free-ranging chickens is noteworthy.
On the picture of Savanna II, my falconry red-tail, viewers can see the soft cere directly between the eyes. It's only slightly yellow, not nearly as intense as in wild red-tails. Savanna is copiously fed with turkey necks, occasional pigeons and sparrows, and a vole or mouse every now and again. She's very healthy, but because she's not eating three to five wild-caught voles each day, she's not getting large amounts of plant pigments found in the rodents' stomach and intestines in the plant foods they consumed. Savanna gets veterinary vitamins, minerals, and trace elements I give her to supplement the raw proteins and lipids of her diet. She's in superb health, should anyone be concerned.
The photo also shows her tan breast, which I alluded to a day or so ago. In the Midwest and East, most adult red-tails have a rather white breast, and the neck area beneath the chin is also white. This bird, and a few others from Ohio, are genetically dark-breasted, as I mentioned. Expert viewers from the West would say that this bird is colored very much like typical Western red-tails, but it was hatched here in Ohio. When I go to a falconry event in Indiana or Illinois, just one or two states to the west, I note the very different color patterns of the red-tails from those states. Across the continent, red-tail colorations vary in minor ways within populations. Feather colors are all genetic and can help identify individual birds and variant local populations, such as the red-tails of Central Park.

John A. Blakeman