Friday, January 07, 2005

THE RAISIN-BREAD HYPOTHESIS

THE RAISIN-BREAD HYPOTHESIS

A few days ago one of the Central Park hawkwatchers reported that she had seen Lola at the Azalea Pond with an immature redtail in close proximity who was "mantling" a squirrel [Mantling means covering the body of some previously caught prey with the wings] The hawkwatcher assumed that the bird was one of the young from the 2004 nest.
"How did you know that the immature hawk was one of the 2004 kids?" I asked, "Did you recognize it by some field marks?"
"No," answered the hawkwatcher, "But it HAD to be one of the kids because Lola tolerated it in her territory. I assume that she would chase away any unrelated bird."

I wondered what John Blakeman might make of this report, and asked him , by e-mail, whether it was odd to have one of last year's young still around in the Ramble at the beginning of January.
He answered that it would be highly unusual, even "weird", and the next day followed up with the letter below:

Marie,

The chance that the recent immature is one of last year's offspring would be only that, pure chance – and rather unlikely.

There is no way that Lola or Pale Male could (or would) recognize the new bird as one of their progeny. Yes, that happens with social mammals, where parents imprint to the smells or other identifying clues of the young. But that sort of thing doesn't happen in hawks. Lola didn't fail to confront the new bird because she recognized it as one of her beloved offspring. “Belovedness” rapidly evaporates in mid- to late summer when eyass feeding behaviors are no longer hormone driven.

I believe I mentioned in an earlier note that RTs are famous for becoming slightly social in early winter, meaning that adults will allow other RTs, mostly unpaired young adults (“floaters” we call them) and first year birds to occupy prime winter hunting habitats.

I think that's what's being seen in Central Park. Lola just sat there while the immature mantled her catch. While doing so, Lola was looking around and she also had seen numerous rats and squirrels in the park. She was also completely fattened from abundant food that she paid no attention to the intruder. Remember, for a hawk, food is life.


In my Western studies in Nevada, raptor biologists out there have a wonderful habitat concept called the “raisin bread” theory. In early summer there are abundant ground squirrels that provide abundant food for nesting RTs. But mid-summer drought sends these mammals back underground to pass the drought in a hibernation-like state. By late summer and into the fall, there are few prey animals for the RTs to capture, and except for the very capable old adults, immatures get hungry (well, they start to starve) and that always compels young hawks to migrate.

But scattered across the Idaho and Nevada deserts are isolated desert marshes. In the raisin bread theory, these are the “raisins.” As the RTs (and others) encounter these islands of refuge, they drop in to hunt the abundant voles there. Hundreds of diurnal raptors can be seen at some of these in early winter.

The same phenomenon may occur at NYC. Central Park is a raptor raisin, a winter raptor food oasis, an area with a large, available prey supply within a larger region devoid of prey. This new intruder just happened to see the food, too, so she* decided to stay and take advantage of the mammalian offerings. Lola, fat as she was, paid no attention. This is rather common, as I said, at this time of winter.

But in a few weeks, that will change altogether. As the sex hormones take effect, Lola will not allow any intruder in her territory. It's always something of a spectacle in watching an adult resident drive off an intruding bird. There is seldom, if ever, any physical contact (an event falconers call “crabbing”). Usually, the adult simply flies over and displays her body in a way that is easily discerned by the intruder. The immatures almost always get the body language of the adult. If the adult lands nearby, she will bow her head and lift her wings a bit. This is called an intra-specific threat display, and the young bird recognizes instantly. It's the look every Catholic nun used to give errant 8-year old boys when they should have been doing their arithmetic lessons. The youngster responds rather quickly.

But the real story here is that Lola isn't making any threats. She's comfortable allowing the intruder her hunting discretions. This is further testament to the ample prey in Central Park. The pair produced two and three eyasses for nearly a decade. That, alone, indicates the large supply of food animals. Lola's seasonal disregard for this new intruder is another one.

I doubt that the intruder was a bird hatched at 927. And even if it was, the parents would not have recognized it as such.

Hope all of this brings some light.

(*The sex of unknown hawks are always female, a grammatical convention of falconers that extends from Shakespeare's time. The word “falcon” specifically applies to the female peregrine; the male is the “tiercel.” And in red-tails, 55-60% of fledged first year birds are females.)

Sincerely,

John A. Blakeman

THE RAISIN-BREAD HYPOTHESIS

THE RAISIN-BREAD HYPOTHESIS

A few days ago one of the Central Park hawkwatchers reported that she had seen Lola at the Azalea Pond with an immature redtail in close proximity who was "mantling" a squirrel [Mantling means covering the body of some previously caught prey with the wings] The hawkwatcher assumed that the bird was one of the young from the 2004 nest.
"How did you know that the immature hawk was one of the 2004 kids?" I asked, "Did you recognize it by some field marks?"
"No," answered the hawkwatcher, "But it HAD to be one of the kids because Lola tolerated it in her territory. I assume that she would chase away any unrelated bird."

I wondered what John Blakeman might make of this report, and asked him , by e-mail, whether it was odd to have one of last year's young still around in the Ramble at the beginning of January.
He answered that it would be highly unusual, even "weird", and the next day followed up with the letter below:

Marie,

The chance that the recent immature is one of last year's offspring would be only that, pure chance – and rather unlikely.
There is no way that Lola or Pale Male could (or would) recognize the new bird as one of their progeny. Yes, that happens with social mammals, where parents imprint to the smells or other identifying clues of the young. But that sort of thing doesn't happen in hawks. Lola didn't fail to confront the new bird because she recognized it as one of her beloved offspring. “Belovedness” rapidly evaporates in mid- to late summer when eyass feeding behaviors are no longer hormone driven.

I believe I mentioned in an earlier note that RTs are famous for becoming slightly social in early winter, meaning that adults will allow other RTs, mostly unpaired young adults (“floaters” we call them) and first year birds to occupy prime winter hunting habitats.

I think that's what's being seen in Central Park. Lola just sat there while the immature mantled her catch. While doing so, Lola was looking around and she also had seen numerous rats and squirrels in the park. She was also completely fattened from abundant food that she paid no attention to the intruder. Remember, for a hawk, food is life.


In my Western studies in Nevada, raptor biologists out there have a wonderful habitat concept called the “raisin bread” theory. In early summer there are abundant ground squirrels that provide abundant food for nesting RTs. But mid-summer drought sends these mammals back underground to pass the drought in a hibernation-like state. By late summer and into the fall, there are few prey animals for the RTs to capture, and except for the very capable old adults, immatures get hungry (well, they start to starve) and that always compels young hawks to migrate.

But scattered across the Idaho and Nevada deserts are isolated desert marshes. In the raisin bread theory, these are the “raisins.” As the RTs (and others) encounter these islands of refuge, they drop in to hunt the abundant voles there. Hundreds of diurnal raptors can be seen at some of these in early winter.

The same phenomenon may occur at NYC. Central Park is a raptor raisin, a winter raptor food oasis, an area with a large, available prey supply within a larger region devoid of prey. This new intruder just happened to see the food, too, so she* decided to stay and take advantage of the mammalian offerings. Lola, fat as she was, paid no attention. This is rather common, as I said, at this time of winter.

But in a few weeks, that will change altogether. As the sex hormones take effect, Lola will not allow any intruder in her territory. It's always something of a spectacle in watching an adult resident drive off an intruding bird. There is seldom, if ever, any physical contact (an event falconers call “crabbing”). Usually, the adult simply flies over and displays her body in a way that is easily discerned by the intruder. The immatures almost always get the body language of the adult. If the adult lands nearby, she will bow her head and lift her wings a bit. This is called an intra-specific threat display, and the young bird recognizes instantly. It's the look every Catholic nun used to give errant 8-year old boys when they should have been doing their arithmetic lessons. The youngster responds rather quickly.

But the real story here is that Lola isn't making any threats. She's comfortable allowing the intruder her hunting discretions. This is further testament to the ample prey in Central Park. The pair produced two and three eyasses for nearly a decade. That, alone, indicates the large supply of food animals. Lola's seasonal disregard for this new intruder is another one.

I doubt that the intruder was a bird hatched at 927. And even if it was, the parents would not have recognized it as such.

Hope all of this brings some light.

(*The sex of unknown hawks are always female, a grammatical convention of falconers that extends from Shakespeare's time. The word “falcon” specifically applies to the female peregrine; the male is the “tiercel.” And in red-tails, 55-60% of fledged first year birds are females.)

Sincerely,

John A. Blakeman

Monday, January 03, 2005

A CHALLENGE TO CENTRAL PARK HAWKWATCHERS

A CHALLENGE TO CENTRAL PARK HAWKWATCHERS
FROM JOHN BLAKEMAN: YOU TOO CAN BE FIELD SCIENTISTS!

I SENT JOHN BLAKEMAN THE LATEST OF LINCOLN'S PICTURES SHOWING THE NEST WITH A GROWING NUMBER OF TWIGS.[SEE BELOW] HE SENT THE FOLLOWING REPLY, FULL OF FASCINATING INFORMATION ABOUT REDTAIL NEST-BUILDING HABITS. HE ALSO INVITED CENTRAL PARK HAWKWATCHERS TO SEND IN SOME OF THEIR OBSERVATIONS. AN EXCITING CHALLENGE.


Marie,

Yes, I just checked out the new nest site image, with both birds on it, and I smiled again. These birds are doing just what most experienced, red-tailed pairs should be doing right now, on schedule. As you know, I've never much doubted the fidelity of this pair to this refurbished nest sub-structure, and now that extends to the emerging nest itself. All is well.

Let's watch and see what happens. The pair isn't going to waste any time or energy with any tentative alternate nests. That happens sometimes in the wild. This pair is now totally re-committed to 927 Fifth Ave.

But here's something to watch for. Nest construction is likely to proceed in one of two modes. Rural birds usually start selecting a nest site in earnest about now. That's what's happening with this pair. But many other pairs dawdle around with a meager pile of sticks for a week or so, then all of a sudden, in a day or two, they bring hundreds of sticks to the nest, causing it to pop up to full size rather instantly. I've been in the field on a late January day, discovered a new low nest like the 927 on one today, then came back a day or so later, and little more had transpired. Upon resumption of nest observations in February, still not much more.

But when I've skipped two days and come back, a full-sized nest is in place. Instant nest. Let's watch to see if Pale Male and Lola get into one of these "let's build the house in a day" modes. It's very likely they will.

Someone should be measuring (estimating) the height of the nest at the end of each day and creating a graph on this. If someone can email daily images, I can easily do this on my CAD program with an accuracy of an inch or less. If someone can measure a brick the same size as the one behind the bird, we can easily figure out the dimensions. From just looking at the bird itself, I can estimate dimensions. Such nest-building data would be really fine field observations. And if a day or so is missed, we can interpolate. I'd be glad to post the readings every four or five days.

The alternate, less exciting mode is the go-it-slow one, where the nest just gets put together at a leisurely, incremental pace. That can happen, also. Let's see which method the pair chooses (And they might do something I'm not familiar with, too. We can all learn.)

The other observation of the immature bird eating suet is plainly weird. If I offered a piece of suet to my red-tail, she'd give me that "How dumb do you think I am?" look, sneering in absolute repugnance. I can understand how the Park hawk might have taken its first bite of the suet. The suet was obviously placed in the Park for other birds, and as I always contend, red-tails sit around and see and contemplate everything. It saw a woodpecker on the suet, and noticed that it looked like the winter fat it consumes on the squirrels and rats it eats. So yes, it could have taken a single evaluative taste. But to pull up the entire chunk and go off and eat from it is unheard of. Red-tails just don't consume much fat. And they aren't particularly enamored of beef products, especially those with lots of fat. (Don't try to feed a red-tail ground beef or hamburger. Too much fat.)

Another Central Park red-tail mystery.

One last point. Apparently another RT pair had an active nest in CP last year. For authentic ecological understandings of red-tails in CP, I think it would equally valuable to monitor the activities of all other CP red-tails this year. I'm impressed that Pale Male and Lola allowed another pair to reside and nest in CP. How these two pairs interact will be very interesting. Are they communally hunting throughout CP (unlikely, as RTs are very territorial)? If not, which pairs are hunting where, and with what success? How have the two pairs partitioned the small hunting territories of CP? That's important, because if a second tree-nesting (or other) pair becomes as experienced and stable as the 927 pair, the new pair might begin to claim more territory, perhaps some that Pale Male and Lola now claim. That could reduce the availability of food to feed the offspring, which could, in turn, reduce the brood size to a more normal one or two.

As I mentioned in a previous note, this is rather equivalent to the noteworthy predator/prey relationships of the great cats on the savannas and grasslands of east Africa. You NYC people get a better chance of studying this than I do out here in rural Ohio. My RT territories are 2-4 sq mi. I've got to be traveling all over the countryside to see adjacent pair interactions, if any are to be seen at all. You fortunate folks need merely to rotate your spotting scopes, or to walk a block or so to another part of the park.

Look, the CP red-tails are no longer just a wonderful urban curiosity. They are legitimate wild denizens of a major human ecosystem, the Park. It's time their behaviors be documented and quantified. I no longer question the persistence of CP red-tails. They are with us for the present, and I think for the future, too.

Let's see how this year progresses. It's February. Let's see when the first copulation is noted. (And it's not "mating." They did that several years ago by forming the pair bond, the social relationship.) All of us, including hawks, are noting the increased day length. The testosterone and estrogen (well, mostly just the testosterone) are starting to ooze. Copulation will start soon. Somebody, keep track of copulation events by time of day and site. Do they have preferred times and locations for red-tail sex, or are these things just rather random? For red-tails, how is "Sex in the City?" I'm betting that the raptorial thing is every bit as engaging as that of the show. And now, there may be two CP pairs to observe.

See why we observational field biologists have so much fun? We can all get into the red-tail's mind when we see and understand what they do in their daily lives.

I've run on a bit here again. Got to get back to work.

Keep us all posted.

Sincerely,

John A. Blakeman

Sunday, January 02, 2005

difference between mating and copulating

After receiving the correction from John Blakeman about my use of the word "mating" as a euphemism for the word "copulating, I e-mailed him back to say that I was just trying to be unnecessarily delicate, but that I knew what they were doing on the various rooftops and antennas of Fifth Ave. I also sent him a copy of Red-Tails in Love, which I began to realize he had not read. [It was never a book directed towards scientists, after all.]He wrote back the following letter, which I thought extremely thought provoking, and important -- a wonderful and profound letter:

Marie,

I well understood that you (and most others) recognized the difference between mating and copulating. And I also understand the discretion that might be appropriate in presenting any of this to the public.

Bt given both the birds' profligate sexuality, and that contemporary uses of exact sexual terminology are not now so socially egregious, I think the public should be prompted to recognize the distinctions.

I say this because those of us who have worked with these nonsocial, solitary predators always marvel at their socializing behaviors when pair bonding. All of what you described, the vocalizing, sitting close together, and especially food sharing, are so counter to normal, day to day red-tail behavior. As both a falconer and a raptor biologist I get to see both a) normal hunting behaviors (in my hunting red-tail) that are solitary and decidedly nonsocial, compared to the b) social mating behaviors during the extended breeding season which has just begun.

I marvel at how the birds restrain their solitary and predatory behaviors when pair bonding. Red-tail copulation is interesting enough, but is not so remarkable as the complete turnaround in pair bonding behaviors. The public use of the two terms will prompt the hawk watching public to discern the importance of the bonding behaviors. It's important that observers not arbitrarily or casually ascribe human or mammalian explanations for any red-tail behaviors, especially the "lubby-dubby" behaviors that are now beginning seen. It's love all right, but very different from that of social predators such as dogs, or the ultimate primate, humans.

People need to understand that red-tailed hawks are altogether unique unto themselves. They are not a mirror or model of any other species. Their nobility is their own. And again, your book, I'm sure, has conveyed that. I look forward to reading it.

Sincerely,

John A. Blakeman