Saturday, July 16, 2005

Blakeman: Fledging dates are way off!


Yesterday I posted some statistics about Red-tailed Hawks' fledging dates, and applied them to the Trump Parc nestlings. According to those statistics redtails take their first flight from the nest [that is, they fledge] 42 to 46 days after hatching. That set of numbers is what is sometimes called the window of opportunity. All scientific accounts of bird species gives you such a window for each species. It gives a range--the earliest possible number of days from hatching and the latest, for fledging. American Robins, for instance, fledge 14-16 days after hatching; Bluejays, 17-21 days; Red-bellie3d woodpeckersd 24-27 days; Ospreys 48 - 59 days.

I never questioned the window 42-46 days for Red-tailed hawks because during all the years I observed the nest at 927 Fifth Ave I could never tell for sure [nor could anyone else] when exactly incubation began or when the chicks hatched.
We always made educated guesses, based on the hawks' behavior. When a baby fledged later than 46 days after we had decided a baby had hatched, well, we figured, our educated guess was wrong.

Even when I sent out the "Window of Opportunity" posting yesterday, something seemed wrong about it. For instance, the babies of past years at the Fifth Ave. nest always began to jump up and down vigorously and flap mightily in the days before fledging. The Trump Parc babies have just barely begun to stand on their two legs in an uypright position. Until a few days ago they were still sort of crawling around on the nest. Their flapping is brief and weak.

Still, my strong belief in scientists' greater knowledge [excuse: my father was one], made me abandon common sense and post the item predicting that the Trump Parc babies could fledge any minute.

Below are two letters I just received from John Blakeman. I don't always agree with him, [as you'll see in tomorrow's posting]. But I agree entirely with what he writes in the two letters that follow:



First letter:

Marie,

I don't mean to discount the published fledging periods you posted, but for this pair, in this year, at this location, they are way off.

There is no way either of these birds is going to successfully loft into the Manhattan air anytime real soon. The last posted date is next Tuesday, the 19th. I've watched both captive and wild red-tail eyasses mature on nests, and these birds are at least 10 days from fledging, probably closer to two weeks or more.

The flight feathers of the wings and tail are still "in the blood," partially grown with active vascularization within. They are very heavy right now, compared to the very meager thoracic flight muscles. That's why the birds will flap just a few times at this stage, then stop or just plop down exhausted. The wing feathers are heavy, filled with blood. When dry and mature, they are -- light as a feather. But not yet.

Neither the birds' muscles nor feathers are within a few days of the maturity required for actual flight. The coverts, or smaller feathers covering the wings and body are just beginning to emerge. Neither bird presents any workable aerodynamic profile.

So let's not get our hopes up prematurely. Like an infant taking his first toddle, fledging for observing humans is always an exciting moment. But it's fraught with all sorts of threats and challenges, especially in the city.

As eager as everyone is for fledging, I prefer to see the birds hang around on the nest for as long as possible. If either bird has done her reading and wishes to diligently follow the published dates, I hope she lands safely. The more likely outcome will be for the birds to follow instinct, not older, invalid-for-NYC data.

Let's keep our fingers crossed on all of this. Red-tails are large, strong birds that frequently rise to any challenge. Let's see if these two birds can. So far, all is well.

Sincerely,

John A. Blakeman


Second letter:

Marie,

I'm not familiar with the work giving the fledging dates you posted. In fact, I never really quantified the days in the nest for the birds I studied, primarily because I couldn't determine exact days of hatching. Either I wasn't in the field watching the nest on the hatching dates, or, in the manner of the 927 nest, it was difficult to see what was actually happening way up there. My captively-reared eyass didn't fledge in a conventional manner at all, being raised in a cage.

At any rate, I'm wondering if the posted dates are for authentic fledging, the taking of a first flight, or do they refer to the eyasses walking out of the nest onto the supporting limbs of the tree. Falconers are familiar with this process, and for centuries eyass goshawks have been taken for falconry just when the young birds start to climb out onto limbs. The birds are then affectionately referred to as "branchers," having stepped out onto adjacent branches, but not fully feathered or able to fly.

The Trump Parc eyasses are just getting to the "brancher" age. If they were in a conventional tree nest, they would very likely begin to edge themselves delicately out on to larger limbs or branches, thereby "leaving" the nest about now. They would hop right back into the nest at night, but they become ever more venturesome in their pedestrian excursions as their legs get stronger.

Perhaps this is what the author meant. If so, the dates are correct -- except of course in our urban cliff-side nest lacking any branches. But I'm sure the birds have been seen to be wandering about on the ledge. Bipedal mobility precedes winged mobility. I think we have a pair of "branchers" about now.
Sincerely,

John A. Blakeman

PS from Marie: The reference book I cited was The Birds of North America, an authoritative text first published species by species and recently completed for all species of North American Birds. It is published by the Academy of Natural Sciences, the American Ornithologists' Union and the Cornell Laboratory of Ornithology.

Blakeman: Fledging dates are way off!

Yesterday I posted some statistics about Red-tailed Hawks' fledging dates, and applied them to the Trump Parc nestlings. According to those statistics redtails take their first flight from the nest [that is, they fledge] 42 to 46 days after hatching. That set of numbers is what is sometimes called the window of opportunity. All scientific accounts of bird species gives you such a window for each species. It gives a range--the earliest possible number of days from hatching and the latest, for fledging. American Robins, for instance, fledge 14-16 days after hatching; Bluejays, 17-21 days; Red-bellie3d woodpeckersd 24-27 days; Ospreys 48 - 59 days.

I never questioned the window 42-46 days for Red-tailed hawks because during all the years I observed the nest at 927 Fifth Ave I could never tell for sure [nor could anyone else] when exactly incubation began or when the chicks hatched.
We always made educated guesses, based on the hawks' behavior. When a baby fledged later than 46 days after we had decided a baby had hatched, well, we figured, our educated guess was wrong.

Even when I sent out the "Window of Opportunity" posting yesterday, something seemed wrong about it. For instance, the babies of past years at the Fifth Ave. nest always began to jump up and down vigorously and flap mightily in the days before fledging. The Trump Parc babies have just barely begun to stand on their two legs in an uypright position. Until a few days ago they were still sort of crawling around on the nest. Their flapping is brief and weak.

Still, my strong belief in scientists' greater knowledge [excuse: my father was one], made me abandon common sense and post the item predicting that the Trump Parc babies could fledge any minute.

Below are two letters I just received from John Blakeman. I don't always agree with him, [as you'll see in tomorrow's posting]. But I agree entirely with what he writes in the two letters that follow:



First letter:

Marie,

I don't mean to discount the published fledging periods you posted, but for this pair, in this year, at this location, they are way off.

There is no way either of these birds is going to successfully loft into the Manhattan air anytime real soon. The last posted date is next Tuesday, the 19th. I've watched both captive and wild red-tail eyasses mature on nests, and these birds are at least 10 days from fledging, probably closer to two weeks or more.

The flight feathers of the wings and tail are still "in the blood," partially grown with active vascularization within. They are very heavy right now, compared to the very meager thoracic flight muscles. That's why the birds will flap just a few times at this stage, then stop or just plop down exhausted. The wing feathers are heavy, filled with blood. When dry and mature, they are -- light as a feather. But not yet.

Neither the birds' muscles nor feathers are within a few days of the maturity required for actual flight. The coverts, or smaller feathers covering the wings and body are just beginning to emerge. Neither bird presents any workable aerodynamic profile.

So let's not get our hopes up prematurely. Like an infant taking his first toddle, fledging for observing humans is always an exciting moment. But it's fraught with all sorts of threats and challenges, especially in the city.

As eager as everyone is for fledging, I prefer to see the birds hang around on the nest for as long as possible. If either bird has done her reading and wishes to diligently follow the published dates, I hope she lands safely. The more likely outcome will be for the birds to follow instinct, not older, invalid-for-NYC data.

Let's keep our fingers crossed on all of this. Red-tails are large, strong birds that frequently rise to any challenge. Let's see if these two birds can. So far, all is well.

Sincerely,

John A. Blakeman


Second letter:

Marie,

I'm not familiar with the work giving the fledging dates you posted. In fact, I never really quantified the days in the nest for the birds I studied, primarily because I couldn't determine exact days of hatching. Either I wasn't in the field watching the nest on the hatching dates, or, in the manner of the 927 nest, it was difficult to see what was actually happening way up there. My captively-reared eyass didn't fledge in a conventional manner at all, being raised in a cage.

At any rate, I'm wondering if the posted dates are for authentic fledging, the taking of a first flight, or do they refer to the eyasses walking out of the nest onto the supporting limbs of the tree. Falconers are familiar with this process, and for centuries eyass goshawks have been taken for falconry just when the young birds start to climb out onto limbs. The birds are then affectionately referred to as "branchers," having stepped out onto adjacent branches, but not fully feathered or able to fly.

The Trump Parc eyasses are just getting to the "brancher" age. If they were in a conventional tree nest, they would very likely begin to edge themselves delicately out on to larger limbs or branches, thereby "leaving" the nest about now. They would hop right back into the nest at night, but they become ever more venturesome in their pedestrian excursions as their legs get stronger.

Perhaps this is what the author meant. If so, the dates are correct -- except of course in our urban cliff-side nest lacking any branches. But I'm sure the birds have been seen to be wandering about on the ledge. Bipedal mobility precedes winged mobility. I think we have a pair of "branchers" about now.
Sincerely,

John A. Blakeman

PS from Marie: The reference book I cited was The Birds of North America, an authoritative text first published species by species and recently completed for all species of North American Birds. It is published by the Academy of Natural Sciences, the American Ornithologists' Union and the Cornell Laboratory of Ornithology.

Thursday, July 14, 2005

Hawk Aerodynamics



Anne, a reader of this website, saw a picture of Charlotte on Lincoln's website and hoped that John Blakeman would comment on it. I forwarded her query, and he sent a long response. Below is the first half. I'll post the remainder tomorrow.


Dear Marie,
There is presently on Lincoln's site an excellent photograph of
Charlotte flying (dated 6.11.05). [It] is great because you can see the curvature of her wing tops, the leading edge, & it makes the physics of 'lift' so clear. Everyone is surely focused on those eyasses and their amazing development but could you ask John Blakeman (at some point when he has a moment) to address the specifics of her wings and flight? I'm particularly interested in the wing tips with separated bending feathers. I've read that they are anti-stall at low speeds (like a canard?) but I don't understand how this works.
Thanks much,
Anne

Anne, and everyone,
Some comments on the red-tail’s wings and flight feathers.
The very first thing to understand about a soaring red-tail is that its wings are not locked or set into position, although they appear to be. When soaring, the bird appears to be flying with great ease. That it is, as it isn't flexing its strong thoracic flight muscles, consuming energy. But it's wings and feathers aren't locked into position, either. The bird is presumed to have pressure- and position-sensing nerves at the base of all of the large flight feathers, continuously sending flight information to the brain. If a gust of wind strikes the bird's extended left wing, the brain (or spinal cord) instantly responds with signals to feather-position muscles, telling them to properly reposition.
If possible, with binoculars or a spotting scope, try to close in on a slowly soaring red-tail. You will note thousands of tiny, rippling wing feather readjustments. For a red-tail (and other raptors, too), staying in the air requires continuous, microscopic tweaking of feather positions, accomplished by hundreds of small muscles attached to the flight feathers.
We've all folded a sheet of paper into a glider and given it a successful toss. But if we were to make any sort of model red-tail and give it a toss, it would spiral to a quick crash. Flying for a red-tail is a markedly active endeavor. Whether just soaring with set wings (but not set feathers), or alternately in muscular flapping flight, the bird is actively adjusting feather positions and attitudes (angles of attack).
Right now, as we watch the two Trump Parc eyasses begin to extend and pump their wings, keep all of this in mind. Of course, the primary purpose of these exercises is to strengthen the large flight muscles connecting the wings with the breastbone. But the birds are also beginning to develop and refine their feather control nerve reflexes. When an eyass jumps into the air for the first time, it has to have some literal feeling of where its feathers are and its ability to effectively readjust them. When you see the clumsiness of the eyass's first flights, laugh if you will (I do). But understand that the bird is still learning new nerve reflexes. You excited your parents when, for the first time, you stood up and staggered off for a few erect steps. Just as humans must minutely adjust leg and torso muscles merely to stand, red-tails must do the same to wing and tail muscles merely to soar.
About the long, end-of-the-wing primary feathers. Yes, these finger-like, projecting feathers are spread apart when the hawk soars. In a dive or in rapid flight, they are pulled together to form an extended single wing surface. In the spread, open position, each primary feather acts individually like the long wings of an albatross. The open-fingered primaries extend the effective lengths of the wings, yielding great lift. But because a soaring bird moves slowly through the air, the outer wing surface would stall out if the air stream had to pass over the entire outer wing surface. Instead, it can pass slowly and individually over each feather finger without stalling. It's just good, adaptive aerodynamics.
The extended primaries also assist when the hawk is landing. As it slows to take a perch, the bird has virtually no forward air speed, and therefore very little lift. Without the extended, high-lift outer wing feathers, these big birds would tend to crash when landing.
One other set of feathers to note – but usually only for an instant when landing or taking off – are the alulas (“AL-u-lahs,” singular “AL-u-la”), the small, short feathers that lay over the “wrist” of the wing, where a thumb would attach if birds had one. In normal flight, either flapping or soaring, the alulas are held flat on the top of the wing. But when great lift is required under stall conditions, usually when landing and taking off, the alulas are thrust up to smoothly direct air back over the top of the slowly moving wing.
Sincerely,
John A. Blakeman

[more Blakeman on aerodynamics tomorrow]

More on Hawk Aerodynamics: Blakeman

In yesterday's query to John Blakeman Anne mentioned an aeronautical term unknown to me: canard. Below, the Ohio biologist gives some informatioin about that term. Then he offers more thoughts about hawk flight. He writes:

Marie,
From a Google dictionary:
canard \kuh-NAHRD\, noun:
1. An unfounded, false, or fabricated report or story.
2. A horizontal control and stabilizing surface mounted forward of the main wing of an aircraft.
3. An aircraft whose horizontal stabilizer is mounted forward of the main wing.
Because red-tails tend to move the outer feathers of their wings forward during soaring, the outer primaries act very much like canard wings.
The alulas, the smaller projecting feathers at the "wrist" also act as canard wings when the bird is landing, smoothing the flow of air over the wing at low speed, when it would otherwise break up and create drag and lose lift. Very complicated aereodynamics, so I will have to be careful in what and how I state things. I'll defer to any aeronautical engineer who weighs in on the subject. But the key matter is that the hawk is in continuous control and minute modification of its feather and wing attitudes. If we had a stiff, mounted red-tail in perfect soaring postion, even with perfect weight distribution, we couldn't toss the specimen off a tall building and expect it to glide with stability to a distant landing. The bird model would go immediately into a spiraling, uncontrolled crash. Not much different from the balance refinements of a ballarina. Looks easy and perfect. It's hard and
Sincerely,

John A. Blakeman