Friday, June 02, 2006

Re-posting letters from John Blakeman and Chris Lyons

Many readers have written in about problems getting this posting [below] on the website today. I've removed all formatting on the posts, eliminated the photos, and am posting these extremely interesting texts again. Hope this works.

Two fascinating letters below, one by John Blakeman, the other by Chris Lyons, a new website correspondent whose reports on the redtail family at Fordham University often appear on The City Birder, Rob Jett's website about Prospect Park.

For those searching for some good, not very mathematical reason to discount the monstrous geometric progressions indicating that Pale Male might now have offspring numbering in multiple digits, naysayers can ask if Pale Male was the only red-tail siring offspring. Obviously, there were tens of thousands of other breeding males who also produced ample offspring in the last decade or so. If all of them had the breeding successes of Pale Male, the entire surface of the world would be covered with them (or something). More seriously, if Pale Male's progeny proliferated in any way, what might have been their selective advantages? What might it have been about Pale Male's offspring that could have caused them to succeed in any way better than those of other males? Having a colorful, even orange-ish breast conveys no advantages I can think of.

Personally, I think red-tail eyasses fledged in Central Park probably have some significant disadvantages against their rural-hatched brethren. When Central Park yearlings leave NYC in their end-of-summer migrations, they necessarily must make their livelihoods out in wild, rural areas -- where they have no real experience or understanding of the non-urban threats and challenges there.

A young Ohio actress who goes to New York City to enter the theater business has to learn a lot of things quite foreign to her childhood in a small Ohio town. Conversely, a New York red-tail trying to survive its first winter in some wild, rural area somewhere in a Southern state will have equal challenges. Knowing red-tails as I do, I really think a Central Park immature red-tail has things really stacked against her. She's never even seen a vole, let alone learned where to hunt for one. (Voles are the sustenance food of rural red-tails.) Rural pigeons are virtually impossible to catch, as they don't sit around in large flocks eating provided grain. There are rats in the countryside, but they have the good sense not to wonder out in the daylight. In short, urban red-tails trying to make it through their first year in the rural wild have multiple disadvantages that their rural-hatched relatives don't. The rural birds learned out to survive out there in June and July while still being tended to by their parents. Central Park yearlings learned how to live in Central Park, and that's very different from being able to capture sufficient prey on in the wild in the cold winter.

In short, I honestly doubt that many of Pale Male's offspring have gone on to breed. Certainly no inordinately large class of them have. The realities of first year survival in rural and wild environments must be a part of any long term survival equation. The multiplication key on the calculator isn't the only one that must be punched. The division and subtraction keys are also very prominent in calculating the probabilities of survival. Again, I don't think NYC-hatched red-tails have anything going for them when they get out into the rural wild. It's a tough world out there.

--John Blakeman

Christopher Lyons adds:

Could I just add a quibble I haven't seen yet?

Obviously it's fun to speculate about the maximum number of descendents Pale Male could have, even though we know it's wildly out of touch with reality. But it's ignoring the fact that these theoretical
hawks are not just Pale Male's descendents.

Every single eyass that fledged from 927 Fifth Ave was only 50% Pale Male.

While some inbreeding may occur in this species, as John Blakeman has said, we can assume that most of his kids hooked up with unrelated Red-Tails, either by leaving the immediate area, or finding a territory
nearby, and attracting a mate from Red-Tails being born in nearby areas, or coming from up north to spend the winter, or passing through in migration.

So by and large, Pale Male only provided 25% of the genes for his grandkids.

And with each passing generation, his genes are diluted. By the time you got to tens of thousands of descendents, you'd be talking about hawks who were maybe 1% Pale Male--and 99% other birds. And in the evolutionary sweepstakes, that's a win--you win if your genes survive. Better to have a lot of descendents who are a LITTLE bit you than a few who have a larger dose of your genes. The phrase about not putting all your eggs in one basket comes to mind, but that's probably inappropriate in this context.

The entire North American Red-Tail population has been estimated at 300,000 individuals, by the way--which may be low. But whatever the number is, it's unlikely to have gotten much larger since Pale Male was hatched. So a lot of other Red-Tails were propagating their genes as well.

We don't have enough data on this species to say with authority that Pale Male has had an amazingly high number of offspring--above average, certainly, particularly when compared to Red-Tails living in more wild settings. But with Red-Tails breeding in so many urban and suburban areas across North America, it may well be that many other Red-Tails have had equal or higher breeding success rates. They just didn't have such a visible piece of real estate, with so many ardent observers present.

One study I just read a summary of estimated that out of 1,000 Red-Tail eggs laid in one breeding season, there might be as few as 40 living Red-Tails ten years later. And it's entirely possible that's an

It's possible Pale Male's young have a higher survival rate--but so would all the other hawks colonizing urban and suburban areas with higher prey densities. These hawks have genetic agendas of their own, and would be competing with Pale Male's descendents for
territories and mates, often successfully. And judging from the photographic evidence I'm seeing, probably a lot of them have orangey-chested eyasses, and would have had even if Pale Male had never bred.

Btw, this morning I took a look at "Raptors of the World", by James Ferguson-Lees and David A. Christie. The color plate in that book that covers Red-Tailed Hawks was done by Kim Franklin--who is a guy (the book is British in origin, though published here by Houghton Mifflin) There is one illustration of a juvenile Red-Tail. And that bird has definite orangey color on the breast, though it's starting to fade.

Annoyingly, the text in the book doesn't go into detail about the plumage changes of developing eyasses. They clearly had no idea what a matter of vital significance this would become. ;)