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.