Friday, May 06, 2005

Blakeman answers a few questions

I sent John Blakeman the following questions the other day:

Since April 19 was an exceptionally hot day here in NYC, is it possible that the mantling behavior observers saw on that day did not signify that a chick had hatched but rather, that it was very hot up there and it was time to cool the eggs off. To continue that line of thinking, might there still be some eggs up there that were, for one reason or another, non-viable?

Blakeman answered:

I don't really think the mantling was a result of high air temperatures on that day. They might have risen to even the mid-80's (probably not at that height, where there would have been mixing with cooler transverse winds), but that’s still not hot enough to get the birds to rise off the eggs in a mantling posture. Red-tails are very capable of changing their metabolic rate to maintain constant body temperature. We know that at night they can drop body temps to the low 90s, and it can go to around 105 or more after physical exertion. Remember, they cool themselves not only by breathing air through the lungs, but also through the extended air sacs attached to the lungs. They even extend out into the larger bone interiors. If it get hot up there (and mid-80s isn't really uncomfortable for a sitting red-tail, the bird just breathes a bit deeper and slows food metabolism.

When a red-tail over heats, it will open its mouth pant, something that anyone watching could have seen. I didn't see any of that in any of Lincoln's images, and I don't recall anyone mentioning panting being seen.

Now incubating red-tails do get up off the eggs from time to time during incubation, occasionally for apparently inordinate periods of time, up to 20 minutes or so. We think this is done to allow more oxygen to diffuse into the egg. But whenever it’s done, the parent moves some nest lining around and over the eggs to keep them relatively warm. In my experience, they don't mantle over an unmoving egg. They keep their wings normally folded.

My next question was about the spikes: On Lincoln's photos we can see that the spikes on the nest site are not really sharp and pointed , but in fact have blunt rounded ends, like little circles. How could they have damaged the eggs? Blakeman answered:

About the spikes. Yes, they have rounded-over tips, not sharp points. Red-tail eggs for the first 3 weeks of incubation remain quite thick and stout. During that time, puncture by the prongs is not so likely. But in the last week, the eggshell thins to allow the chick to crack the egg with its egg tooth. I'm certain that the prongs could have cracked the shell during this period, even though not pointed.

The great question, of course, is what are the birds sitting on now, long after incubation should have terminated with hatched eggs. . .
In fact, there might still be a single infertile and intact egg in there creating the continued incubation. That’s not at all unreasonable. If the egg were infertile, or if it lost viability early on, the eggshell remains thick and perhaps unharmed.
The only way to know any of this is to dangle a mirror or webcam over the 926 roof line. But I doubt that that can, or should, happen. And even if that were to happen, nothing really could be changed. I may be all wrong. There may be three intact, prong-cooled dead eggs up there. Or, three prematurely-hatched corpses, or a combination of both. Makes really no difference. The birds are going to come back nest winter and refurbish the nest no matter what, adding another layer of sticks. They surely will not just sit down and lay eggs next March without attending to the lengthy sticks-to-the-nest routine. Those behaviors are essential lead-ins to actual egg laying, so there is nothing anyone can do now. It’s all just academic, and it may not be useful to prolong the controversy by continuing to post my musings on it.

Note from Marie. The emphasis above is mine. I think that is the crucial thought here: It is not important to try to look into the nest, or to find precise answers to our nagging questions. The birds will add a new layer next year, and the outcome, we hope, will be better.

I agree with John. Let's not prolong the discussion of what exactly went wrong with this year's nest. I'm hoping we can move on to the many other fascinating aspects of Red-tailed Hawk behavior, physiology, psychology that we haven't by any means exhausted yet.

Monday, May 02, 2005

Blakeman on today's Photo


This photo, taken on May 1, 2005, was posted on this morning. John Blakeman, [who checks in to both Lincoln's and my website daily,] scrutinized it and sent the following letter:

The picture today on Lincoln's site showing an immature red-tail closing in on Pale Male is interesting. First, the bird is a male. Notice that it's just about the same size as Pale Male. A first-year female would be markedly larger. Birds in their first year's plumage actually appear a bit larger than adults. Notice the slightly longer tail on the pursuing bird. First-year birds have slightly longer flight feathers, both in wings and the tail, because they are not quite as strong as adults, so they need more wing area for good flight and soaring.

Observers should never think that birds just fledged are "small babies." In just size, they are larger than the adults of the same sex. They have longer flight feathers. But they are not nearly as muscular and weigh less. Building strong flight and leg muscles is a major process for the birds in their first year. Longer feathers accommodate this.
Notice also that the pursuing immature has two gaps in its wings. Its molt has begun. The first two wing feathers have dropped, and Lincoln's photo shows a black spot at the base of the lost feather opening. This is the new feather beginning to descend. It will take about two weeks for both to grow down and harden. In the meantime, the new feathers are said to be "in the blood." They are rather delicate and can be easily broken. If so, they do not repair themselves. The feather injury and deformation lasts until the next molt next spring. This is why feathers are molted one at a time over many months. The soft new feathers will be protected by the hard old adjacent ones. When the new feathers harden, an adjacent old one will drop. Molting will continue well into September or October, depending on the individual.
Our adults will soon loose their first flight feathers and open gaps will be seen soon. Adults usually begin the molt later than immatures. They don't always drop all their feathers, especially the coverts, the smaller body covering feathers. Close inspection of adults will often reveal two-year old contour feathers.
By the way, should anyone happen across a gorgeous red tail feather (or any other) that has been dropped, refrain the strong impulse to retrieve it and take it home. Yes, the feathers are beautiful, and that's why they were used so extensively on women's hats a century ago. Wholesale slaughter of wild birds for fashion usage nearly wiped out a host of species. Had it not been for the National Audubon Society's efforts, along with others, wild bird protection laws such as the Migratory Bird Treaty Act would not have passed. Even more species would have gone extinct. But remember that the Migratory Bird Treaty Act (and other laws) deliberately prohibit the possession (not just the killing) of listed species OR THEIR PARTS. You cannot legally pick up a hawk (or blue jay, or northern cardinal, etc.) feather and take it home, for any purpose. (Pigeons, English sparrows, and starlings are exempt from the MBTA.) In all but one case (to follow), let the feather sit. You will save yourself a lot of law enforcement trouble.
I imagine only one acceptable case where anyone should retrieve a red-tailed hawk feather. If anyone happens to be watching a Central Park red-tail preen on its roost, and you see a large feather fall and can retrieve it, do so. If you can, try to identify the hawk from which it dropped, preferably Lola or Pale Male. Try not to touch the base of the feather. If you can, put it in a clean plastic bag. Then call the New York state wildlife authority (I'm an Ohioan, so I don't know specifically what it is, but your fish and game authority, or department of natural resources will be listed somewhere. A Google search will pop it up quickly.) Indicate that you have retrieved a known feather from a known Central Park red-tailed hawk and that you request information on how it should be donated so DNA analysis might someday be done on it. Probably no one presently is doing such studies, but DNR should wish to archive the feather for future studies. Specifically, ask the authorities how you should properly dispose of the feather, especially given its important provenance.
All of this is an outside possibility, but more people watch roosting and preening red-tails in Central Park than probably anywhere else. And the DNA of the red-tails there are more valuable and interesting than anywhere else, too.
One other observation. There is the smallest little gap, a very slight V at the center, trailing edge of the photo's immature red-tail. I'm betting that if the bird were to have fanned it's tail, a gap would have been seen there, too. A single tail feather has also been dropped.
And another note. For those who watch hawks elsewhere, where other species of buteos are seen (such as the red-tail, the red-shouldered, the rough-legged, and the broadwinged hawk), it's sometime difficult to identify a bird coming right at you, or in the dismal gray light we so often have in the Midwest and East. Here's how to positively ID a red-tail, of any age (as shown on Lincoln's photo). Only red-tails have a dark patagium, the leading edge of the wing from the body out to the first bend or joint. Notice here that both birds have this dark edge. Two fine red-tails. No other North American buteo has the dark inner wing edge.

John A. Blakeman

Postscript from Marie: A few weeks ago, spurred on by Donna Browne, I spoke to someone at the Natural History Museum [AMNH] about a possible study that would do DNA analyses of the various Central Park Redtails. The purpose would be to try to understand if any of them are related. The initial response was very positive! Now to write a proposal...