Monday, October 24, 2005

Blakeman: Pale Male's kids: red. Grandkids: white or red. And nix on diet

Photo by Bruce Yolton
Trump-Parc nestlings, July, 2005
From John Blakeman:

If all the Central Park eyasses are direct descendants from Pale Male, and he's homozygous dominant (2 dominant erythrism genes), all of his first generation offspring must necessarily be erythritic.
The greater question arises in his grandchildren, who are most likely to be heterozygous, having both a gene for erythrism coming down from Pale Male and a white-breastedness gene from a normally-colored mother. These birds will all be erythritic, but can pass on some hidden white-breasted genes. Therefore, depending if the mother was Ee or ee, we ought to start seeing either 25% or 50% of the grandchildren with white breasts. At the beginning, in the first generation of offspring, all will be erythritic. But in the second generation, the grandchildren, about either a half or a fourth should be white-breasted, depending on if the mother had a single erythritic gene or not.
But there haven't been many grandchildren yet, perhaps just the two Trump Parc eyasses this year. Therefore, the universal predominance of erythritic birds is still very probable and understandable.
Again, all of this points very strongly towards Pale Male's genetic primacy. He's apparently the Man, the patriarch of all the nesting Central Park red-tails.
It will be interesting to attempt to determine the genetic line of the first white-breasted eyass. I think we've got a pretty good handle on it now, awaiting such an appearance.

About there being dietary explanation for the marked breast coloration of the Central Park eyasses and immatures. I'm certain that this is not a factor. First, the birds aren't being fed or capturing anything other red-tails don't take elsewhere. Yes, the CP hawks have learned to take pigeons with greater frequency (and success) than any other red-tail population I know of. But I've fed wild-caught pigeons to multiple red-tails, including eyasses in my research, and I'm certain they don't change feather colors. Rats and squirrels don't change feather colors at all, either.

The breast feathes of most red-tails tend to whiten as they age, even in the first year. I think this is plain environmental bleaching, the effects of sunlight and being out in the weather. With a wild red-tail in hand during the molt, we can easily tell feathers that are newly descended and older, unmolted ones. The old ones are a bit bleached. This can happen to lighter-colored breast feathers.

The dark color of Central Park eyass breast feathers is genetics, not a pigment in the food. Yes, in flamingoes feathers are colored by pigments consumed in food. Not so in red-tails, I'm certain.
John A. Blakeman

PS from Marie
If the noun is erythrism, is the adjective erythritic [JB's preferred version] or erythristic
[mine]? Actually, the American Heritage Dictionary gives the adjectival form as erythismal!