Will the cold be bad for the eggs? John Blakeman says no
While Donna's in Wisconsin, Katherine Herzog has been monitoring the Fifth Ave. nest. She had the question, below, for John Blakeman, which Donna forwarded to Ohio:
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.