Sunday, March 10, 2013
Tom was good enough to allow me to stop by on my way to PA, and I did. This is a quick Droid snapshot of their backyard, a woody place indeed. Tom has created a virtual arboretum, and as we shall see, it doubles as a cageless aviary.
HERE and HERE.
I've wanted to lay eyes on this cardinal since Tom first shared photos of it, and made an attempt last year. After waiting and watching for three hours, I gave up, a defeated man. Jeffrey does not constantly hang at the feeders. He is quite intermittent in his visits, and usually doesn't stay long. However, we scored quickly this day - he popped in just minutes after my arrival and returned once or twice. All told, he wasn't there long though, and I didn't have the opportunity to leisurely click off lots of shots.
This cardinal is exhibiting a condition known as xanthochroism, a genetic anomaly that causes an excess of yellow pigments to show through. It may be caused by darker pigments being suppressed, thus permitting less dominant colorations to shine through.
If we are to get a bit propeller-headed here, the bright red plumage of Northern Cardinals is caused by at least nine different carotenoid pigments. Knock one or some of them out of whack, and we can end up with the bird in the photo or something similar. In my previous post, there is a (bad) photo of a heavily leucistic Red-tailed Hawk. That bird is displaying the effects of yet another genetic anomaly, but one that causes the individual to appear much whiter or paler than normal.
Carotenoids occur in plants and some animals, and birds uptake them as part of their natural diet. It's possible that xanthochroic individuals, like Tom's cardinal, result from dietary deficiencies. A well-known example of the role of carotenoids and bird coloration involves flamingos. If deprived of the blue-green algae and brine shrimp that are rich in beta carotenes that gives them their bright pink plumage, the birds become pale and whitish. By providing captive flamingos with a compound called canthaxanthin, the rich pink coloration can be restored.
Xanthochroism has been documented in a number of bird species, in addition to Northern Cardinals, including: House Finch, Cape May Warbler, Scarlet Tanager, and Red-bellied Woodpecker.
The oldest documented wild Northern Cardinal reached nearly 17 years of age. This fine golden specimen is already at least five years old. With luck, it will live for many more years, delighting all who are fortunate enough to see it.