Sunday, February 06, 2005

BLAKEMAN ON THE PROLIFERATION OF CP REDTAILS

BLAKEMAN ON THE PROLIFERATION OF CP REDTAILS
and
BLAKEMAN ON PROGENY -- i.e. Are all those CP redtails Pale Male's kids?

followed by CORRECTION OF MY MISTAKE

Marie,

The plot thickens. In December, when I came upon the Central Park red-tails, I learned only of the famous 927 Park Ave pair. Then a bit later, I saw tangential references to another pair that attempted a nest in the Park proper. Now I learn that there have been a total of three pairs residing or hunting in the park recently. When will the surprises end? Back in the ‘90's I thought that any nesting RTs anywhere in NYC would be unlikely, and surely un-persisting. Red-tailed hawks just don't nest in major urban centers – period. At every turn, I've been wrong on virtually every initial understanding of things red-tail at Central Park. I'm pleased to admit my errors, especially when they are corrected by the observations of so many local hawk watchers. What they see is more significant that what I say. I'm merely prognosticating at a great distance based upon my rather different rural red-tail experiences. Hard field data can't be argued with.

I will have to pull up the map of Central Park and try to orient the locations of all three pairs now. Initially, I thought the presence of a single pair in such a small place to be unlikely. But three pairs live there. Utterly remarkable. This is likely to be the highest population density of the species anywhere in the East. In areas of the West with high ground squirrel populations, red-tails frequently occupy territories of about 0.5 sq. mi. Central Park is 800 and some acres, as I recall, and a square mile is 640 acres. Three pairs in approx. 800 acres yields a territory size of approx. 0.40 sq. mi. In the wild grasslands of the West virtually all of the open ground space is occupied by ground squirrels. But so much of Central Park has no hunting habitat. The actual prey habitat of the park is only a fraction of the total size. (There’s another master’s thesis, describing habitat and prey utilization by red-tails in central Park.) Any way it gets sliced, there must be a lot of continually available rats and pigeons. I'd still love to learn what all of these hawks are eating, and how they capture their prey. It’s not anything like rural birds. (Suet?)

What do I make of the territorial encounters? They are very important. They cause all the birds to understand where each is “allowed” to be. Keeps the peace. These events, as aggressive and disruptive as they might appear to be, are not at all. This is part of the fabric of red-tail social interactions, ever bit as much as any human choosing to open or close an apartment door after someone knocks. I liked the characterization of “being herded.” Although it appeared that physical contact almost occurred, this seldom happens. The entire business is wonderfully ritualized with the wheeling around, the screaming, the dives, and occasionally some real physical contact. But even that is usually ritualized, as both birds usually grasp opposing legs and talons for an instant before letting go.

Occasionally there will be a powerful attack on an intruder that blows off some feathers, causing the unresponsive bird to retreat in obvious distress. Such intruders are inevitably birds of the year that haven't yet learned the protocols of red-tail property rights. Just one or two of these incidents sets the youngster aright, and she then behaves herself appropriately. One of my falconry red-tails saw a new immature sitting in a field overlooking my bird’s frequent hunting area. Savanna wasted no time and flew over and knocked the youngster off her limb. She retreated quickly. The next day the same bird was sitting in the same tree. But just as soon as Savanna and I stepped into the field a quarter mile away, the youngster immediately flew off. She learned a lesson from my grand matriarch hunting companion. When required, the same lessons are taught to inattentive intruders by wild birds such as Pale Male and Lola. From the description of this territorial conflict, all parties behaved with appropriate deportment, as proper New Yorkers would, of course.

Again, a record of when and where and which birds are involved in these aerial displays would be invaluable in discerning habitat utilizations.

Now to the question everyone romantically ponders. Have any of the interlopers been sired by Pale Mare? Do the parents recognize their offspring and therefore accommodate their adjacent presence. It sure would make a better story if any of this were so. But it makes little biological sense. I'm guessing that few, if any, of the other RTs seen in Central Park are 927 offspring. Here’s why.

In virtually every case in rural areas, adult red-tails deliberately drive off the season’s young in July or August. When things start to get hot and there is no longer any hint of spring (meaning that prey animals also are getting harder to find and capture), parents stop feeding the fledged eyasses and actually drive them away, if required. Most of these youngsters have the same feelings toward mom and dad as we did when we were 18 or 19 and they are glad to fly off to new horizons, un-pestered by weird parents.

I am absolutely certain that neither parent is able to recognize its progeny in subsequent years. That happens in social mammals, of course. But none of this is in the limited behavioral abilities of these birds. Their brains aren't set up for such recognition. Sorry.

The summer’s “leave-the-house" behaviors persist throughout the year. The birds just don't have any genetic or behavioral compulsion to return to their natal territory. Why go back home? Mom and pop will come right out and give them “that look”. Red-tail populations that faithfully returned to natal territories to attempt to breed drastically limited their choices of mates. After a few years of this, the only potential mates were siblings and cousins. Biologically that makes everybody similar, and that becomes a genetic defeat. Biologically, it’s best to mate with someone reasonably unrelated, to minimize genetic deficiencies and maximize genetic variabilities and the consequent behavioral opportunities. Who wants to date his sister? Who wants to have mom and pop riding herd, or flying over them? Again, the compulsions to return to a red-tail’s growing-up neighborhood are pretty weak.

But of course, I admit to being initially wrong on so much of the Central Park red-tails. The fact remains that any of the other birds, could indeed, be Pale Male’s progeny. I can't deny that. Could be. Probably not, however.

For now, we have to guess. This is why it would be nice to get many of these birds banded. Because this is a special population worthy of special study, colored marker bands should be used, allowing easy identification with spotting scopes. The fact that Pale Male is so easy to identify has been crucial in understanding the entire population. How helpful it would be to have all six or so of the CP red-tails color-banded. And the progeny question would be answered immediately if all the eyasses were banded on the nest or soon after fledging. If the birds were banded, we'd really have a handle on so many questions.

I don't recommend that the 927 eyasses be banded on the nest. Getting to the nest would require the re-installation of the dangling structure (What was it, the swing platform, or something?). But in the wild, in open rural areas, the young could be easily trapped and banded when they start to hunt in June and July. (See my description elsewhere on how that is done, causing no harm whatsoever to the hawks.) I'm not sure this could be done in Central Park, however. The complications are multiple and I won't delineate them here.

As a biology major I tried (how mistakenly) to stay away from literature classes where I would have to figure out the ever-convoluting plots of the great novels. But that’s exactly what we have here. Our real-life novel now has some other personalities. I thought the story was to be only Pale Male, Lola, and their annually departing (I think) offspring.

But some more chapters are being written by our hawks. This is going to be a good tale.

Sincerely,

John A. Blakeman

Correction of facts in my reply to John Blakeman

Here's what I wrote:

One pair made a prolonged but unsuccessful nesing attempt last spring in a tree a little north of the Great Lawn They may have already begun to incubate eggs before the nest was somehow destroyed.[Let's call them the Great Lawn pair]. The male of that pair was exceptionally light in color and was popularly called Pale Male Jr.

Another pair hangs out at the southern-most border of the park,[59th St.] and is often seen perching on buildings on Central Park South: the Trump building, and the one with the green roof next to it especially. They have been seen bringing nesting materials to a building ledge last year and the year before that-- another prolonged nesting attempt.[Let's call these the CPS hawks] A birder named Ben Cacace who works in that neighborhood had very detailed observations of their activities.

Well, I didn't mean The Great Lawn. It was actually a tree a little North of the Heckscher Ballfield, and just a little south of the 66th Street Transverse. So let's call that pair the Heckscher Ballfield pair.

Now it appears that last year, the pair I referred to as the CPS pair was regularly pursued by a pair of peregrine falcons that hangs out near the top of a building at 5th and 59th St. It seems more than likely that the CPS pair simply moved into the park to get out of peregrine territory and made a nesting attempt near the Hecksher Ballfield. SO...scratch the CPS pair. They and the Hecksher Ballfield pair are one and the same.


Oh yes, another thing: There is probably yet another redtail pair at the northern-most part of the park, somewhere around 110th St. and the Harlem Meer.

GOOD NEWS: A hawkwatcher named Karen Anne Kolling is working on an e-mailable map of Central Park with all hawk territories marked on it. As soon as she sends it I'll post it on this site.