Wednesday, January 30, 2008

Blakeman illuminates the spike situation - Post #3

Photo by Donna Browne - enlarged detail (showing spikes) of Blakeman's red-dotted photo below

This morning I e-mailed John Blakeman and asked him the following question (referring to Donna Browne's photos I had posted earlier in the day:) John: Is there any way to explain (specifically if possible) what there is about these photos that indicates the problem that the spikes posed to the eggs? I'm sure readers would like to have this illuminated.

Blakeman's response, along with the photo below:

The attached photo indicates the problem with the pigeon spikes. It was taken by Donna Browne in early January. I entered the photo on my CAD program, zoomed in, and placed a red dot over each of the visible spike tips. Without this magnification and spike marking, there doesn't seem to be much of a problem.
But it was this marked photo, I believe, that sealed the necessity of getting up to the nest and removing the spikes, at least the ones directly in the center of the nest, in the lined nest bowl, where the eggs are incubated.
The red dot just to the left of the left-most egg is revealing. Not only is the prong sticking up into the space where the eggs would have been rolled (impossible because of all the protruding metal spikes), but the closest magnification (here obscured by the added red dot) reveals that the spike shaft actually extends directly to the right, under the egg. The egg is actually wedged or perched right upon this metal spike's shaft.
The red dot immediately to the right of the eggs also appears to mark a spike that bends back, directly under the eggs.
Actually, there were almost surely many more spikes slightly buried under the lining material, which probably expanded during summer rains and wind events. Back in March, when the eggs were laid, it is very clear to those of us who have seen Red-tail eggs and nests that the prongs both prevented proper rolling (a crucial factor in egg hatching) and they also directly touched the resting eggs, wicking away incubation heat to the metal cradle frame and screening below.
Both of these now-obvious factors, the eggs resting on the spike shafts, and the fact that the spikes extended up above the nest lining, thereby precluding proper rolling, virtually assured incubation failure.
Once again, there are three essential factors in successful hawk egg incubation. One, humidity and moisture loss from the porous eggshell, was not a factor. Lola's naked brood patch took care of that factor. But keeping the eggs at sufficient, enduring temperature, and properly and frequently rolling them, were both impossible with the spikes extending into the egg space, as I previously contended for a year or more.
Now, with the spikes in the central bowl gone, the eggs will not be a few degrees too cold in cool March nights way up there above Fifth Ave. And when Lola feels a compunction to roll the eggs of her developing children, she will be able to do that naturally and instinctively. She will be able to push an egg outward, spin it around, and then nudge it back into place under her brood patch. Before, the spikes absolutely prevented that.
Again, in summary, originally the eggs became lodged between the spike shafts down in the lining, thereby precluding proper rolling and temperature maintenance.
Now, I think we have a great chance of seeing eyasses once again take to the skies above Central Park. Let everyone rejoice when that happens!
--John A. Blakeman