Tiresias, the blind singer
While his name is Tiresias, I do not expect him, after being transformed into a woman for a finite time, to report that the female Zebra Finches enjoy sex 10x more than the males. Tiresias is not only blind; he hatched without fully developed eyes. This is a case of congenital unilateral anophthalmia or perhaps more accurately, sesquilateral anophthalmia.
It is not that he is “searching with his good eye closed“, 23 October 2009
On the left, Tiresias exhibits primary anophthalmia, as there seems to be no ocular tissue at all. One of Tiresias’s sisters and clutch-mate was born with bilateral primary anophthalmia, and she lived for less than one month, before passing away of what I suspected was an unrelated or else only secondarily related condition. Tiresias’s other four siblings do not exhibit any signs of ophthalmic abnormality.
On the right, Tiresias exhibits secondary anopthalmia. Ocular globe tissue is observable and deeply set in the orbit, and there is even a functional eyelid, as can be observed in the video posted below.
I have not yet concluded whether or not this development is a semi-eye or a quasi-eye. At first, I was convinced that he could detect light to some extent, but lately, I am not so sure. I think that he is aware of me when I approach his cage, but not by sight (and probably not by clairevoyance of his namesake), rather by alarm calls of his relatives.
Tiresias is currently in good health, otherwise. He is active and capable of finding food and water as soon as I serve it. He also demonstrates a good appetite for the moistened pellets that I feed to Bulbuls (Zupreem AvianMaintenance™ Cockatiel pellets). He does not fly, though he is mechanically capable. And he is quite vocal now that he is mature.
I have read of such cases before, and I had the suspicion that this is the sort of thing that only occurs in the flocks of careless finch keepers who allow excessive consanguinity. Typically, I do not even allow pairing of cousins, even though John Stossel and the National Society of Genetic Counselors say that it is OK. I have been keeping Zebra Finches (in very large numbers) for more than five years now, and I never witnessed such a case, until recently. And strangely, a few months prior to Tiresias’s hatching, there was a different ophthalmic complication with chicks sired by another male Zebra Finch, the one whom I acquired at the same time and from the same breeder as Tiresias’s father.
First and foremost, Vitamin A deficiency or imbalance comes to mind. In retrospect, I did not feed greens as frequently as I used to, but I did still serve boiled egg yolk occasionally before, during, and after incubation time. The other possibility is toxicosis. Anophthalmia and microphthalmia were reported in birds, especially marine birds, as a result of teratogenic Selenium, but I do hope that there is not an excess of Selenium leaching from my plumbing fixtures. While genetic factors cannot be ruled out at this point, I think that I will keep more cilantro on hand for the birds.