Friday, August 19, 2005

How many redtails can live together in Central Park: Q & A

In the next exchange, Mai Stewart asked John Blakeman, [in a longer letter]:,

It occurred to me as I was reading the part about next summer, after PM + Lola have successfully borne offspring, that Central Park is going to begin to get quite crowded -- We now have PM + Lola, PMJ + Charlotte, their 2 fledglings, and there was also some mention, much earlier in the winter/spring, about the possibility of another pair of RTS (altho we haven't heard much about them since).

But if all of the above remain in CP, and PM/Lola + PMJ/Charlotte also reproduce successfully next spring, what do you think will happen? Will they all be willing to put up w/ each other -- or will the older pairs begin to drive away the younger ones?

IF there continues to be enough prey for all (and we have no reason to think there won't be), will they all tolerate each other's presence?

John Blakeman replied :

How will it all end -- or at least, how will the Central Park red-tails reach population stability? Things are by no means stable yet. I originally thought that food would be short in Central Park because there are no voles there. Voles are the staff (or mouse) of life for red-tails virtually everywhere else. But the CP 'tails have learned to successfully take the park's pigeons and rats. Most of Lincoln Karim's recent photos of the immatures show them to have fat, full crops. Those birds are eating very, very well. So far, hunger is playing no part in CP red-tail biology. That's seldom the case in the countryside this late in the season, but New York City has been very good to its new residents. The Big Apple has been a feeding feast for the red-tails.
Therefore, hunger -- at least in the moderate seasons -- isn't likely to play its normal role in causing the parents to drive out the maturing birds of the year. The offspring are likely to extend their residencies as long as possible, even right on through the winter. This birds are so fat that they have no normal compulsion to move on, to get out of the house or apartment as it were. These birds might start to be considered spoiled brats, feeding profusely and easily on the abundant offerings of NYC.
If they are ever driven over to Jersey or anywhere away from the park, these young'uns are going to have a quick ecological comeuppance. Finding and killing wild food out in the countryside is going to present some real challenges for this pair of spoiled kids. There aren't many easy-to-kill rats in the countryside, and even Pale Male himself couldn't capture rural pigeons, who have the good sense not to peck around inattentively at thrown out grain. In the countryside, Cooper's hawks quickly dispatch any pigeon that acts like a Central Park pigeon.
So, what will happen to the Trump Parc youngsters, and the other young red-tails likely to start their hunting lives in Central Park next season? Considered diligence (so far, pretty much lacking on my part) should dictate a plea of ignorance. If the CP red-tail population acted like the normal, rural ones, the fledglings would no longer be fed and would now start to feel the desperate pangs of hunger. Mom and Pop would also start pushing the youngsters off the breeding territory, either by luring them out with dangled food, or more usually by merely neglecting their plaintive cries of food begging. In northern Ohio, at just about the same latitude as NYC, our fledglings are no longer being fed and they are crying out across the landscape for someone to feed them. In desperation they are chasing grasshoppers, and making their clumsy attempts at capturing voles. A few of them will quickly become experts at this and survive the winter. The greater majority will starve in the next month or so. I see a few of these dead birds along rural roadsides and always stop to examine them. They died pitifully weak, as mere skeletons. Sad, but a fact of life for rural red-tails.
Obviously, things aren't going to play out in Central Park as I've described for rural Ohio. We do know that adults in fall and winter are much more tolerant of competitive, interloping birds when their territories have abundant food. And Central Park has an abundance of red-tail food, so how will the expanding RT population stabilize or play out in coming years? That, now, is the greatest remaining red-tail natural history question in the minds of knowledgeable field biologists. So far, there are at least two productive pairs of red-tails in the park. In time, could there be three, four, or five? A year ago I would have said only one pair was sustainable. Now, at least two surely are. I would not be surprised at all if one or two more pairs take up nesting residence next winter.
The real question is how social will well-fed nesting pairs be. How will the adjacent pairs interact with an abundance of food? Could there eventually be six nesting NYC pairs doing their hunting in Central Park? There may be enough food for this, but will the adults learn to tolerate such a number of adjacent pairs? Out here, red-tails commonly have one- to two-square mile breeding territories. In Central Park, could there eventually be a half dozen pairs? Could be, especially if over the coming years there is natural selection for this. In rural areas, there is natural selection for large, isolated, unencroached-upon territories. That arrangement produces the most red-tails annually, over large land masses. But that dynamic doesn't look to be so operative in Central Park. For the red-tails, everything is new and different there.
Does it sound like I'm dodging the question? You bet. Together, let's see what happens next year and the years to follow. The Central Park red-tails are here to stay, that's now certain. Just how many stay is still a question, one that I want to follow. I'm out here in obscure fly-over land, so I can't see the wonderful things you see in the park. Keep me posted. The central Park red-tail story is still only a few chapters long. The closing chapters of rural red-tail accounts won't reveal the final ones of the CP pairs. Nature is still writing the work, so we'll just have to wait until she's done in a few years. A plea of informed ignorance is wisest with this set of birds at this location.


John A. Blakeman