Tuesday, February 19, 2008

John Blakeman and The Plum Brook Station Bald Eagles

Winter lasting a little too long for you? Do you need to remember that August actually exists? Here's a gorgeous view of The Gill, Central Park in August, from nature photographer Eleanor Tauber.
And now for the promised report from John Blakeman on the Plum Brook Station Bald Eagles!

I tried to get into Plum Brook Station on Monday, but it was closed, for President's Day. I wasn't able, then, to discover anything about the 5 Bald Eagles I saw going over the fence into the facility on Sunday.

But this afternoon I went in for a quick look. I toured the entire site, looking for any new Bald Eagle's nest, finding none. I did find a new Red-tail's nest, which I'll also watch. There are probably 6 to 10 Red-tail pairs in the Station. I've spent no time tracking down any of the RT nests.

At the PBS Bald Eagle nest, at "K-Site," the pair was sitting together in a tree perhaps 50 yards from the now-completed nest. The birds weren't hunting, nest-building, or even socializing, just sitting up there and relaxing.

But the pair had been seen in copulation earlier in the day. Because of this, the NASA people presumed that an egg would be therefore appearing in a few days. This is not very likely, as the numerous pre-egg copulations of the 927 Red-tail pair reveal. Red-tails and Bald Eagles (can you imagine this) seem to copulate just for the social (and other) fun of it, long before any real haploid (unfertilized) egg begins to appear in the single fallopian tube of the female.

An egg will be laid at the appropriate time, which isn't necessarily right after copulation. Yes, as I reported yesterday, one of the nearby Ohio Bald Eagle pairs is now sitting on at least one egg. The pair is famous for laying February eggs, among the first in the entire state each year. Why they do this is unknown. Most of the other 120-plus nests get eggs deposited mostly in March. The majority of Ohio Bald Eagles have the good sense to wait for March's warmer weather.

And I think the Plum Brook Station pair is likely to follow that pattern. Things at the nest could be rather mundane for the next two or three weeks. The nest is full-sized now, and probably has a thick complement of lining material.

Although it looks like nothing significant is happening with the pair, other than the increasing number of copulations, this is really a very, very important period of time. The female is now taking it easy, expending only moderate amounts of energy in her hunts. She's looking for some large fish in the Lake Erie marshes, or a dead road-kill deer, both of which can allow her to gorge out. The production of two or three fertile eagle eggs is metabolically taxing, requiring the concentration of a large amount of pure, nutrient-filled lipid, the yellow part of the egg, along with an even larger concentration of dense proteins, the "white." Covering all of this is the shell, the minerals of which are known to be chemically extracted from the mother eagle's own bones.

Therefore, for all of the winter the big female has been attempting to get as fat as she can, loading herself with proteins, lipids, and bone minerals. A tremendous amount of energy must be expended to quickly form (in about two days) each new egg that descends down the fallopian tube. If the female has eaten well this winter, she can lay as many as three eggs. If food has been scarce, she might lay only a single egg.

Those who can closely watch a female hawk or eagle in the middle of egg formation can often note a vacant, distant look in the eye of the bird. Her concentration is no longer focused on prey, perches, or anything else. Her focus is internal. Who knows what it feels like to have an egg slowly descend a long fallopian tube, all the while growing and becoming hard as the shell is laid down.

So, now we wait. It could be several weeks before anything of real interest is visible. The wait will be worthwhile, however.

--John Blakeman
And as I can't quite wait for the Bald Eagles to reappear in my area, I'm going to take a jaunt to the Mississippi River on Friday to see if I can find some open water--and hence, I hope, some Eagles!
Donegal Browne

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