Saturday, March 17, 2007

Blakeman on Cold Weather and Eggs and What Is That Big Bird?

Photograph Donegal Browne
Eldest of the Cathedral Nest
Yesterday, with the weather taking a turn for the worse Katherine Herzog, a faithful daily visitor to the Hawk Bench who's been contributing her observations, thankfully as I'm enmeshed in taking care of rather unpleasant family business in Wisconsin, asked me to send her weather and eggs question off to John Blakeman, the Ohio Red-tail expert.

Here's Kat's question-

Today the temperature is supposed to plummet and they're predicting rain and snow (up to half a foot) for the next couple of days. I thought PM and L had escaped that wrath of winter weather but at least the clutch is complete and the eggs are not as vulnerable as when they had just been laid?? That's the question I have for John Blakeman: Are the eggs more vulnerable (softer?) when they first come out; and are therefore more susceptible to damage when the weather is severe...cold, wind and snow. Or are they impervious to radical temperature/weather changes?

And John Blakeman's answer-


As bad as the weather might be for humans and other un-feathered creatures who have to purchase and don weather-fighting appurtenances, the hawks are well-provisioned for whatever weather might happen. How many times since the Pleistocene (the Ice Age) has there been cold, thick snows in March?

No problem. The feathers of the hawks easily accommodate the weather, and the eggs are tucked in those feathers and touch the warm naked brood patch on the female's belly. As bad as the weather might be for us, for the eggs it will be nicely warm and cozy up in the nest.

And because they are new eggs, the cold weather---should it cool the eggs for a period----will have no effect. First, the eggs are the strongest right now, with a full thickness of shell. As the eyass grows in the egg it produces carbon dioxide, as do we. This soaks into the watery fluids of the egg and forms a dilute carbonic acid, which in the next four weeks will slowly react and consume much of the egg shell. This weakens it, allowing the baby hawk to poke through the egg at the proper time, a process called pipping.

We are a long from that. Now, the egg is strong and firm, allowing the mother (and sometimes the father) to carefully roll the eggs every hour or so. This keeps all of the internal membranes properly suspended. Unrolled eggs don't grow properly and die (a concern with the pigeon prongs, which might keep the eggs from rolling naturally within the nest bowl).

Actually, raptor breeders know that freshly laid eggs can be stored for a few days, even a week or so, at 40 degrees F without harm. The female does this in the nest by sitting higher on her first eggs, keeping them somewhat cool and retarding embryonic development. When the last egg is laid (the second or third where the parents have sufficient food -- just one often in my rural Ohio areas where corn and soybeans predominate and retard mouse and vole populations), the female hunkers down for the beginning of full incubation with the warm brood patch in contact with the eggs.

This process of starting true incubation at the same time for all of the eggs helps assure all of the eyasses will be the same size during growth, allowing a somewhat equitable distribution (or grabbing) of food. This doesn't often happen in golden eagles, where one eaglet almost always grows earlier and faster than its sibling. The larger eaglet always then just kills and consumes the lessor bird. Golden eagles only fledge one eaglet because of this Cain and Able conflict, regardless of the amount of food the parents bring to the nest. Fortunately, it's not so with our less greedy red-tails.

It doesn't matter what the outside temperature or snow mass might be. Against the female's brood patch, all is well.

But nest watchers are likely to note disconcerting periods of apparent inattention as the adults are away from the nest for up to a half hour. We are not sure on this, but it appears the periodic 15- or 20-minute periods of egg cooling are beneficial. As the egg cools down to, say 70 degrees from the 100-degree+ incubation temp, oxygen can diffuse into the egg at the reduced temperatures. Periodic cooling is probably very important.

So don't be alarmed when the nest is left unattended for short periods in the coming weeks.

Somehow, it all works.

--John Blakeman
What is that BIG bird?
It's was yet another chaotic day of attempting to make order and rational sense out of chaos. Seemingly impossible sometimes but we just have to keep on trying.
I wondered why there had been so few pigeons and doves around the grain elevators. It seems the state has elected to allow a hunting season for them for, as I've heard it said, people don't like them sitting on their churches. (Forget me, Francis of Assisi would be utterly mortified. )
So the soft gentle coos, the morning low note in bird song is mostly missing and has been replaced by more and more and more Starlings making their various strident noises. The Grackles have started to come through and with them various Blackbirds, I even heard a Red-wing today, but mostly it has been hundreds of thousands of Starlings darkening the sky, scavenging the corn fields bare, and mobbing the grain elevators.
I'm once again motoring down the road between the town where I stay and the nursing home where my mother currently lives watching these immense clouds of Starlings and thinking of how few woodpeckers and other cavity breeders I've seen this year. The sun is low in the sky creating that golden light so beautiful on the buildings of Fifth Ave which I am not there to see, and I'm also morosely thinking about how all those Starlings were hatched in cavities where a native bird might have laid eggs. And even more morosely thinking about the fact that I've not seen one Bald Eagle yet this year though Wisconsin is number three for Bald Eagle population in the U.S. I'm definitely as they would say around here, "down in the dumps".
When suddenly far far, we're talking way down the road, I see in the sky...what? A Red-tail flapping? Looks kind of big and kind of wrong. Two ducks almost neck and neck flying in unison. Not a chance.
I'm trying to zoom up there before whatever it is, is lost in the trees, when the bird, as if on cue, rounds it's wing tips down to brake, veers towards me, the sun hits it, and zap, sizzle, the body gleams gold and by golly that's a bright white head! I veer over myself onto the shoulder far faster than I should have and watch this marvelous bird drop her talons and glide in a slow balletic descent across the river.
Another set of thoughts cross my mind. Okay, so now the balance of nature is off with too many Starlings, we humans can be such idiots, but given my druthers I'll take that over not enough Eagles.
Donegal Browne

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