Saturday, October 22, 2005

The mystery of Pale Male's and Junior's orange-chested kids

photo by Cal Vornberger - May 29, 2004
Fifth Ave. nestling, jumping
Photo by Lincoln Karim -- September 1, 2005
Trump-Parc fledgling [f], pondering

Yesterday I posted Part I of my investigations into the mystery of the orange-red coloration of all Pale Male's offspring, and of the similar coloration of the Trump Parc hawk kids.Here is the question I asked famous hawk rehabilitator and field researcher Len Soucy in an interview a few hours earlier: Is orange-red the usual breast color of the thousands of young redtails you've seen over the years, or is it something particular to the Pale Male offspring? I only had a chance to post the question. Then I had to make a train to Conneecticut.I promised to reveal Len's answer the next day.

On the train back last night I checked my e-mail device and found an anticipatory message from John Blakeman. Here it is. After that, at last, a summary of what I learned from Len:

Like the rest of us, you've got us on the edge of our seats awaiting Len Soucy's response to the question of the prevalence of local red-tailed hawk immatures with golden, orange, buff (or whatever -- non-white) breasts.

As you noted, colored breasts on the immature red-tails of Ohio and most of the entire Midwest are very, very uncommon. In reaching my previous conclusion that the Trump Parc eyasses were probably Pale Male descendants, I presumed that the dark breast color was not common in the New York area, either. But in honesty, I've never studied red-tail populations of the East. That's why I suggested reference to someone who might be familiar with regional color patterns. Immature red-tails are famous for getting into trouble in their first summer or fall and many end up in rehabilitation centers. The people who run these places see lots of local immature red-tails. So Len Soucy's pronouncement will be authoritative.

Frankly, I'm hoping that this color pattern does occur in local red-tails. That, of course, would deflate the romantic familial relationships we've pretty much presumed for the Central Park red-tails. As a story, it would be nice if Pale Male, Sr., were indeed the patriarch of the many red-tails now seen in the park. But from a biological perspective, it would be far better if several unrelated adults were the red-tail colonizers of Central Park. A single line of descent from a single patriarch male, even with several different mothers mixed in, would create a narrow genetic base. It would be far better to have several lines of genetic descent, from multiple parents, populating such a small area as Central Park, or even all of Manhattan.

With the greater genetic diversity of multiple lines of descent (if the hawks are not so closely related), the population is much more likely to survive and thrive. Genetic diversity is a key to the survival of small, insular populations. I'm hoping that I was wrong, that a number of local red-tails have been seen with the darker breasts, indicating a much broader range of genes within the population.

And in retrospect, the fact that virtually all of the offspring have had darkened breasts (at least recently, as far as I can recall) might indicate that the genes for this coloration have been in each of Pale Male's mates, and also in this year's Trump Park mother. This trait may be rather common in the area.

Again, I hope I was wrong, that the birds are not closely related, that they are typical red-tails of the local area.


John A. Blakeman

What Len told me

First of all, Len provided a scientific name for that orange breast coloration that has characterized all Pale Male's nestlings since 1995, and that was seen on the 2005 Trump-Parc nestlings as well: Erythrism -- defined, in the American Heritage Dictionary, as "Unusual red pigmentation, as of hair or plumage." The dictionary accents the first syllable.

" I've handled thousands of redtails at the Raptor Trust," Len Soucy began in a phone interview yesterday morning, "many of them first year birds. I'm also a Field Researcher and since 1969 I've captured and banded at least 10,000 Red-tailed Hawks . Most of the redtails we capture are young hawks that have recently fledged and are making their first migration -- first-year birds.

"The great majority of the young redtails we capture and band are white-breasted birds. Similarly, the young redtails I see at the Raptor Trust, orphans or nestlings that have fallen out of their nests, are predominantly white-breasted.

Very rarely do I see an erythristic first-year redtail. Oddly enough, many of the injured redtails that come to the Raptor Trust as young birds and then stay for longer periods of time [because their injuries are too severe] -- many of these develop that reddish-orangish coloration as they get older. But they started out as white-breasted birds."

Although Soucy insisted that genetics is not his specialty,he was willing to speculate a bit about the mystery of Pale Male's offspring and their unusual chest coloration:

"I agree with Blakeman that it's purely genetic," he said. " And since Pale Male has had multiple mates since 1995, it would appear to be a dominant gene carried by the male. It doesn't make sense any other way."

He agreed with me strongly when I suggested that this common trait makes it more than likely that Pale Male Junior really is a direct descendent of Pale Male [though it is theoretically possible that he is not a son, but actually a grandson]. Len also gave me a few names and phone numbers of other hawk experts, some in the West, who might be more familiar with erythrism among redtail nestlings.. I'll let you know what I learn.

For years we Central Park hawkwatchers have been debating the relationships between Pale Male and the various other redtails we've seen making nesting attempts around the periphery of Central Park. Now we have a strong piece of evidence that at least in this particular case where the nest succeeded and the young were observed, a direct relationship exists. Pale Male Junior is almost certainly a descendent of the famous Fifth Avenue paterfamilias. The other redtails around the periphery are more likely to be offspring too, we have reason to believe; we'll have a stronger clue if any of their nests succeed.

Before I posted this report I wrote again to John Blakeman and summarized Len's information. Blakeman wrote another note:


If erythrism is locally uncommon, then its predominance in the Central Park eyasses raises a number of genetic questions. The fact that all of the recent offspring were erythristic strongly suggests that the trait in Pale Male, Sr. is dominant, and he's homozygous (has two copies of the gene). If so, he's been able to pass down only this trait to all of his f-1s, his kids.
But if his wives, or the mates of his kids don't also have the trait, a few of Pale Male's grand kids should be white-breasted. So far, they haven't been, so perhaps the erythrism gene is also in the unrelated mates. To know this for sure, a few more generations will have to be observed. Pure chance may still be favoring a dominant red-breasted gene. And these things can be influenced by several genes. It may not be a straight Punnett Square genetics problem that we all learned to solve back in high school biology.

PS from Marie
Punnett Square? Is that somewhere near Harvard Square? We obviously missed out at the Bronx High School of Science.