Friday, February 01, 2008

Protecting the Nest and 2007 Eggs Before Retrieval

There was activity on the roof of 927 Fifth Avenue on January 28th. Spring is coming so Pale Male and Lola took special interest in it.

3:29:14PM A workman appears above the parapet on 927 Fifth Avenue.
3:31:08PM With the hormones flowing, the hawks are far more protective than they had been just a few weeks before when the nest photographs were taken. Now, when the workman appears, Lola takes over the nest in a hurry and Pale Male flies back and forth over the roof.

3:31:48PM The workman goes lower, but not quite enough as his red helmet still extends above the parapet.

3:32:17PM Lola focuses on the bowl of the nest which contains last season's eggs.
I'm prone to believe that as the hawks are going to the bowl and looking at the eggs that they do note when they have been removed. The hawks don't display agitated or stressed behavior about not finding the eggs in particular but they do look for them and note their absence after they are removed the next day. John Blakeman disagrees. His thoughts are below at the end of the photo sequence.
Differing opinions are no problem at all. Differing deductions are a common occurrence with observers and something that feeds discussion, the journey toward more understanding plus better hypotheses for investigations yet to come. Discussion and comparison of all data amongst all involved is the life blood of useful investigation and relevant conclusions.

3:32:45PM Lola watches as Pale Male comes in for another pass, this one quite close to the workers heads. Despite how it looks, the workman can't see Lola from their view point and I'm not totally sure if they even realize that Lola is on the nest or that Pale Male is coming in yet again above their heads.

Another pass by Pale Male.

Lola looks to be covering the bowl itself from prying eyes. I'm assuming that is a built in response to seeing those objects in that nest position.

3:32PM Pale Male turns and goes for another look of the roof amd then heads NW.

3:32:33PM Lola watches him go.

3:34PM Lola leaves the nest.

Pale Male curves round Woody Building, and then he lands on the nest. He investigates the nest also looking around as Lola had, and did some staring into the bowl as well.

4:03:11PM The switch. Pale Male takes off from the nest and Lola comes back on.

4:04:01PM Lola investigates the nest, focusing again on the nest bowl.
4:04:19Pm Satisfied with the nest and no workmen in sight, Lola takes to her wings for a cruise in the sky with Pale Male.
These behaviors took place the day before the eggs were retrieved. Beyond the work that was done to the nest carriage, the egg retrieval had an even more immediate positive effect.
Here is what John Blakeman, who worked on early captive breeding trials of Red-tailed Hawks, had to say about why removing those eggs from the nest was so important.

I was pleased to learn that the workmen on the swing stage were able to completely remove from the nest the three remnant eggs from last spring. This was a very positive effort, for the following reasons.

Of course, it might seem that confiscating Lola's eggs, even at this late (or early) date might be disconcerting to her, or to Pale Male. With your photos of PM looking down into the now-empty nest you posed the question he might have been pondering, "Where's those eggs?"

But in fact, neither Pale Male or Lola would have pondered that question following the eggs' retrieval for analysis. While the eggs remained in the nest, they provided a very significant visual cue or prompt for the birds to begin incubation. As the reproductive hormones begin to flow, now that the days are getting longer, the birds will have an urge to instinctively sit on eggs, even prematurely.

In captive breeding experiments, we can dump a white tennis ball or chicken egg in an open nest, and in season the hawks will instinctively begin to "incubate" the objects.

That was the problem with leaving the old eggs in the nest. In late February and into March, weeks before this year's fresh eggs would have been laid, reproductive hormones would have compelled the birds to begin to incubate intently on the eggs they could see in the nest. Just how that, then, would have complicated the new eggs is unknown. But it couldn't have been useful. The nest could have ended up with six eggs, three old dead ones, along with perhaps three new, viable ones.

Lola doesn't have a brood patch on her chest or belly big enough to keep six eggs warm. I was concerned that even after the spikes would have been removed, the presence of six eggs would have compromised the proper incubation and turning of the three new good ones. The hawks couldn't have figured out which was which. They just sit on any white, round object that appears in the nest. Without the removal of the old eggs, it could have been six eggs, thereby disrupting real incubation.

So, it was a good thing the eggs were removed from the nest. The parents aren't sitting around asking each other, "Hey, what happened to those three old eggs that were in the nest all summer?" The birds aren't that cerebral. It's just, if it's there, sit on it. If it's not there, it's not there and there's nothing to worry or even think about.

Now, without the old eggs disrupting normal nest preparation activities, the hawks can go about naturally refurbishing the nest and its lining. When the first egg starts to descend Lola's single fallopian tube in March, both she and the nest will be ready.

--John Blakeman

The second half of the photos from Nest Fix-it Day still to come! As there have been questions, I hope they'll help clarify all the areas from which prongs were clipped.
Donna Browne

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