Monday, February 07, 2005

WHY SO MANY REDTAILS IN NYC?

WHY SO MANY REDTAILS IN NYC?
AN EXCHANGE OF INFORMATION BETWEEN MW AND JOHN BLAKEMAN


Yesterday I sent John Blakeman the map of Central Park with the redtail nesting sites marked that I also posted on this website. It was annotated [baed on my info] and sent to me by Karen Anne Kolling. I added a few observations of my own and some questions. Below is what I wrote to him and his amazing answer:

FROM MW:
John: Below, a map that might be useful to your understanding of the Central park redtail situation.

In summary: we have solid evidence for three breeding pairs: 1. Pale Male, 2. The North Meadow pair [both these pairs had young that fledged], and 3. The failed nesting attempt of the Hecksher Ballfield [formerly CPS] Hawks. The male of that pair is very light-colored and is often called Pale Male Jr. There is another possible nesting pair at the park's north end.

PS Someone has sent me a note reminding me to mention to you that the Central Park hawks do not feed exclusively IN the park. [There are pigeons and rats everywhere in the city, after all.] Pale Male and Lola, for instance, have been sighted on various occasions perching considerably further east than Fifth Avenue-- on Lexington Ave, or even 2nd Ave -- almost to the East River. This would considerably extend the actual size of their territories, perhaps making them conform more closely with the square mile you noted was the usual territorial size.

I might mention one more observation: I live on Riverside Drive, the western-most part of Manhattan. Our apartment overlooks Riverside Park, a narrow strip between Riverside Drive and the river,. We look out on New Jersey. What I'm about to say is VERY impressionistic, but I don't think I started regularly seeing Red-tailed Hawks out our windows facing the river until about ten years ago. Now I and many others see redtails in and around Riverside Park very, very frequently. I am almost certain there is a breeding pair somewhere near my building, though I've never succeeded in finding a nest. Put that together with the fact that before Pale Male arrived in Central Park in November, 1991 [probably on or around Nov. 10th] a redtail sighting in Central Park was a very rare event, something to write in BIG LETTERS in the Bird Register, while today they are as common as robins, practically, and you'll begin to see what an odd situation this is. It looks like a sudden redtail population explosion occurred during quite a short time period.

Cheers
Marie

RESPONSE FROM JOHN BLAKEMAN:

Marie,

Once again, I'm knocked over with your important, new information. You have broached a question that I've pondered but didn't dare raise. Are any of the CP red-tails hunting beyond Central Park proper? Might there even be nesting red-tails elsewhere on Manhattan. If so, and from what you described it sure seems likely, then everything -- I mean everything -- is changed. Could the wild, rural red-tail adapt to a hard-surfaced urban environment that lacks any significant vegetated landscape? The little falcon, the American kestrel did this in the 19th century. But I know of no studies describing this for the red-tail.

Once again, it doesn't make sense. The RT is a big, muscular raptor that so much prefers meadow voles. This prey species may be only marginally present in Central Park, if at all. But it is absolutely absent in the streets and alleys of the rest of constructed Manhattan Island. The incidental perching of red-tails on the edges of back street rooftops in search of rats, mice, and pigeons is moderately reasonable. But how does this giant bird then swoop down and take a rat or pigeon as it darts between pedestrians, taxis, trucks, overhead wires, and all of the other airspace impediments of any modern big city. Red-tails have great difficulty successfully hunting in forests, for this same reason. They can't easily maneuver around tree branches, shrubs, and other vegetational obstructions. That's why red-tails are seldom seen in densely forested areas. When they are, the birds are always perched on the edge of the great forests looking out on to an open forest clearing.

The phenomenon of the Manhattan red-tails is now far more complicated and developed than just Pale Male and Lola. They might actually be the odd couple out, because unlike the others, they don't nest in trees. The other, less-observed pairs may be actually more representative of the red-tail expansion into city centers. The reasons why this is happening needs study and explanation.

Conservationists have lamented the multiple pressures modern industrial society brought against raptors. For decades, in the 19th and first half of the 20th century, raptors where almost universally regarded as vermin. How could a species that rapaciously kills and eats "good" species such as squirrels and cardinals be worthy of respect and protection. Depending on one's view, either God or evolution had made egregious mistakes in allowing the proliferation of these flying criminals. A shotgun could reverse some of that.

But things have changed dramatically, so much so that common raptors have now probably reached territorial saturation, which provides for me the only explanation of the recent incursion of red-tails into NYC. Remember, no one was shooting New York City red-tails in previous decades. Whatever has caused the birds to invade the city, it must certainly have something to do with changed conditions in their normal rural areas. Central Park has always had rats and pigeons and squirrels. It has had mature nest trees for a century. Nothing in either Central Park, nor on greater Manhattan Island has changed as quickly has the red-tail population there. Whatever is causing this new phenomenon, it's something out in the countryside, not in the city. The city has been the same for decades.

What, then, has changed in rural areas? What out there could possibly have prompted red-tails to so dramatically change their natural history? Here's the way I see it And of course, good population studies are needed to authenticate this with hard data -- these are merely my own personal prognostications. (Some of my professional colleagues might object to the public appearance of these here, as they are only private thoughts. But it's good for everyone to form their own thoughts on observed natural history phenomena. I hope these conjectures might prompt others to engage in good, evidence-based thinking.)

First, you are correct in surmising that the many hawks you have been seeing on Manhattan are a very recent occurrence. If any had taken residence years ago, people would have recorded it, with the same excitement you have presented in your wonderful book. A nesting red-tail pair simply can't go unnoticed. Resident NYC red-tails are new. Why?

As a retired high school biology teacher, I recall fond memories of my career, especially the wonderful kids I was privileged to teach. I taught in a school district composed of both rural farm families and conventional suburban housing developments. In the early years of my career, in the 1970s and '80s, virtually all the farm boys had 12-gauge shotguns and .22-caliber rifles. These boys engaged in a great deal of legal hunting and trapping in the Lake Erie marshes. They were as close to the wild as most anyone in the 19th century. These kids would often share hunting and trapping stories with me, asking intelligent biological questions.

Whatever could that have to do with modern NYC red-tails? Everything, I think. Today, virtually no farm kids (what few are left) or other students have the slightest idea on how to hunt or shoot a firearm. In twenty years there has been a major turn of life styles. Formerly, kids spent a great deal of time out in the local woodlots and marshes. From time to time, a few of these boys could not resist the temptation of taking an illegal pot-shot at a passing red-tail. They never killed enough to reduce the population in any detectable number. But they did reduce the average age of the mature breeding pairs of red-tailed hawks. The number of red-tails today in Ohio (and New York and New Jersey) is probably close to what it was after WWII. Before the War, all raptors were shot without restraint. Their populations were decidedly reduced by human predation. With raptor protection laws and enforcement after the War, those pressures were reduced. So the red-tail pretty much saturated all available habitats.

The infrequent killing of red-tails didn't reduce the population, as there was always a large "floater" population of young, unmated birds awaiting a new pair-bonding and breeding opportunity. Every time a red-tail was shot, a new floater quickly filled the ecological void. Remember, all successful species must produce more offspring than can possibly survive. That was a major element of Darwin's explanation ("theory") of evolution. That's exactly why about only one fledged red-tail in four or five ever survives to adulthood. Sadly, most of those wonderful new eyasses that come off the Central Park nests will never survive their first year. Most will drift off and starve. They will never find an un-occupied habitat with sufficient prey for their inexperienced, even meager hunting skills. Old adults have learned all the tricks in capturing a hundred grams of living flesh each day. Young birds have everything stacked against them in this vital quest. Most of the hawks fail.

So, what might occur if very few wild hawks are now being shot, or killed by leg-hold traps? My personal experiences with rural school boys, farm organizations, and others (where I commonly give my hawk protection slide shows) show that this is really the case. Very few hawks are now being killed by humans, and that changes everything.

Formerly, a young red-tail that had learned how to make it through its first winter could merely float around the countryside after its first molt (when it got the red tail and was sexually mature) and try to find an adult that had somehow lost its mate. Because a moderate number of red-tails were being killed by humans, there were a good number of potential new mates for both the rising young adults and the older breeding birds who had lost mates. Raptor biologists are always amazed at the speed with which a new replacement mate appears. How many mates has Pale Male had? How many seasons did he go without a mate? There has always been a new mate waiting for him.

Presently, there are many fewer new-mate openings. Few hawks are being shot. Mated pairs can now grow old gracefully, at age. Red-tails can easily breed successfully for a decade, and some approach 15 years or more. That then (as I see it) is the explanation of the new NYC red-tails. Lots of young red-tails are coming off wild nests every spring. In my state of Ohio, there is likely to be as many as 5000 active, productive nests each spring. With an average of 1.5 fledged eyasses for each nest, that's over 7000 new birds each year. Yes, most of these are going to starve before their first hard winter sets in. But what an abundance of surviving, unmated "floaters" must still populate the wilds of Ohio each year. Where are these birds going to spend their adult years? It can't be out in the countryside, as all available good territories with ample prey are already occupied by experienced adults.

I believe that the red-tails that have recently taken up residence in NYC have come from this saturated floater population. These birds are famous for "floating," drifting around the landscape, looking for something promising. Surely, some of these birds could drift over from New Jersey or down the Hudson and pass over Manhattan. At a nice soaring height of 2000 ft, the trees and "meadows" of Central Park would be easily seen. The abundant prey in the park would also be easily detected.

Why, then, didn't this happen before? Red-tails have always been seen drifting through the park, especially in migration seasons. The major change has been this. Formerly, most self-respecting red-tails simply would not compromise their innate fear of inordinate numbers of 150 lb bipeds strutting about below. Red-tails have enough innate good sense to stay away from the proximity of humans. A transient Central Park hawk visitor soon decided to head back up the Hudson, hoping to find some territorial opening in the landscape. Until recently, these birds could eventually do this. They had no ultimate imperative to try to make it in The City.

But today, they do. Frankly, it's tough out there in countryside. If you thought getting a nice, inexpensive, well-located Manhattan apartment was nearly impossible, the finding of an unoccupied nesting territory may be equally difficult for young adult red-tails. And as so many women know, most of the good men are already married. All the good hawks are already mated out there in the countryside. For a newly-graduated red-tail (meaning that it survived the first winter), there simply aren't many potential mates nor open territories. Therefore, in instinct-denying desperation, a few red-tails have elected to come into the city and see if a life could be made there. And a few of these birds have learned to adapt, to truly make it in The City. Pale Male may have been the vanguard of this new dimension of red-tail life history.

Just as I mentioned in one of my very early essays here, Pale Male has come to New York City and made a success in exactly the manner of hundreds of thousands of human immigrants -- learn the way of the new country, work hard, adapt, and make a new life. Pale Male did it. And now a few other red-tailed hawks are doing it. What a better characterization of one of the great features of New York City?

Please continue to keep me posted on the greater red-tailed hawk population of Manhattan. If this is happening in New York City, it's likely to be happening elsewhere. Most large American cities have central open greenspaces that adaptive red-tails could colonize just as they have done in Manhattan. The text and reference books on American raptors must be re-written again. The first revision was the urban success of the peregrine falcon. Next was the continuing expansion of the bald eagle. Now, it's the urban red-tail. I'm so glad it's happening in New York City -- and that there are so many wonderful people to watch and monitor it. Without your book, this entire matter might have passed unnoticed. Again, thanks so much.

Sincerely,

John A. Blakeman