Sunday, July 24, 2005

Two letters from Blakeman

Below, two communications from John Blakeman.
The second is a copy he sent me of a letter to Donna about a particular observation in her Field Notes:


I share the joy of all in learning that the two Trump Parc eyasses have so successfully fledged. If I might, just a few observations.

First, my thought that the exceptionally high nest location might turn out to be an advantage for the birds' first flights appears to true. In typical rural tree nests, many birds clumsily find themselves on the ground after leaving the nest. Such nests are just 30 to 60 ft above the ground, just a small fraction of the height of the Trump Parc nest. A bird jumping off a tree nest has just a few seconds to get her flying act together before she hits the ground or a much lower limb. Because they were so high, these NYC birds had a lot of air beneath them in which to learn the actual mechanics of flight. They were able to land on nearby building tops, instead of crashing into flexible tree limbs, or the ground itself. This worked well.

It appears that the two birds will now fly between building roofs and window railings and the like. Very soon, they should learn to ascend in flight, and then be able to select desired perches. This is much better than being confined to ground level perches in Central Park.

But I noticed from Lincoln's photographs that at least one of the new fledglings still has a short tail. It's at least an inch less than full length just yet. Therefore, it still doesn't have complete control of the air. Its wingloading is still a bit heavy. Its flight will be labored for another few days.

Charlotte and Pale Male Jr. are typically keeping track of their offspring. The fledglings will make quite a racket to maintain verbal contact.

So far, all appears to be well. After the failure of the 927 nest, we now have success at the south end of the park. It's a gratifying situation.


John A. Blakeman

This note of yours is really significant:

"6:12 Jr. up, circles, flushes pigeons from roofs,
hunting on the fly. Pigeons wheel in front of him and
then bank to around behind him, they gain on him, he
does about-face in air, he's within a hair of nabbing
pigeon but it veers to the side."

This midair direction reversal maneuver may indeed be the secret to the catching of pigeons in flight by NYC red-tails. A red-tail can never capture a pigeon in a straight aerial pursuit. Pigeons can fly faster than red-tails. When tail-chased, the pigeon just flies away from the hawk. Young red-tails will try this in their first hunting exploits when on their own. But they learn quickly that chasing pigeons is a fruitless waste of energy.
The ability of the big red-tail to throw open its wings and tail and turn right back around in a new direction is familiar to falconers who have seen their birds do this when chasing rabbits. Rabbits are famous for running at full speed away from a pursuing red-tail. Then instantly, the rabbit stops and turns around and runs right back where it came from. Young or inexperienced red-tails can't adjust to this instant change in direction and they ignominiously shoot past the rabbit now fleeing backward beneath the hawk. When this happens with my hawk, I always applaud the now-safe rabbit.
But as the bird experiences this more often, it begins to anticipate the rabbit's sudden course changes. That seems to be what Junior is doing.
The most significant thing here is the response of the pigeons. This circling-behind behavior is what pigeons do when they encounter a peregrine out in open air. Peregrines cannot easily make flight reversals with any speed. They just go forward -- at remarkable speeds. If a pigeon can stay behind a peregrine, it is safe. If it finds itself out in front of a lightning-fast peregrine, the pigeon will die.
Consequently, pigeons have ancient instincts to circle around and get behind a peregrine, should one get into their airspace. But pigeons, native to the Old World, have no instinctive behaviors to avoid New World red-tails. Genetically, red-tails are brand new to the pigeon experience. They apparently are trying to use peregrine avoidance instincts to avoid the red-tail.
That may not work, for two reasons. The first peregrine avoidance maneuver of pigeons is to quickly dive into vegetation or hit the ground. Because of their speed, peregrines have to stay out of tree limbs or off the ground. At 80 to 150 mph, a small branch on a tree will break a peregrine's wing. And trying to slam into a pigeon on the ground at such speeds will kill the falcon.
Red-tails, however, are designed to crash into trees and brush, even the ground. They fold their wings and plunge into the vegetation. A pigeon sitting in the center of a tree, believing that it is safe from peregrines, is apparently vulnerable to conniving red-tails.
Your observation of Junior coming close to grabbing a circling-back pigeon is really significant. Red-tails are really intelligent in learning the ways of their prey. Over time, they learn to exploit their perceived vulnerabilities. That seems to be what you observed. Junior may have discovered an instinctive behavioral deficiency in NYC pigeons that he has learned to exploit.
Keep watching. See if you can see this again. This is really beginning to explain why so many pigeons are being taken. This explanation is still mostly conjecture on my part, but knowing the red-tail as I do, this is heading in the right direction (as it were).
Of course, if this explanation is authentic, then how long will it take for the NYC pigeon population to learn not to circle back behind a flying red-tail? Every time Junior plucks off such a pigeon, its DNA that would cause its progeny to do the same thing is lost to the population. A "dumber" pigeon, lacking the get-behind-the-falcon genes won't be killed by a red-tail. Its offspring will likewise survive. Good old Darwinian natural selection. Where might it end?

John A. Blakeman