Wednesday, February 22, 2006

Will the 5th Ave nest succeed this year?John Blakeman answers one of my questions

I wrote John Blakeman with some questions about the prognosis for this year's Fifth Ave. nest. I particularly mentioned people's anxieties about the new "cradle" structure at 927 Fifth put up after the nest and spikes were removed in December, 2004. Here is his reply:

I'm not concerned about the space beneath the nest support structure (the cradle) at all. I've seen a number of tree-crotch nests in the wild that were simply meager in depth. At this time of the year we can often look up through the bottom of nests and see the sky above. This all gets fixed when the birds start hunkering down in the central bowl of the nest and start wiggling around, arranging the nest lining. Before laying, the female will start to pluck out inner down feathers on her belly and chest, creating the "brood patch." In the nest, she puts this naked skin right on the eggs, conducting heat directly to them. Most of the loose breast feathers go wafting away in the breeze, but some are tucked into the accumlating lining material at the bottom of the nest.

When an adult is sitting with its bare breast or belly skin against the bottom of the nest, any whiff of cold air is attended to immediately. This is a primal instinct, to keep the eggs warm. The birds will carefully line the nest with all sorts of fine material and down feathers to keep out the wind. They will take care of this. The opening you see under the nest plays no part in this. The nest is very, very tight just under the sitting female. That's why she spends so much time sitting on the nest and re-arrangeing things before eggs are laid. She's not just passing the day up there. She's making certain that the eggs will be able to stay warm (unless they happen to rest on a metal prong -- which this year we hope doesn't happen, if or when the nest is built higher).

Red-tails have a strong instinct to bring twigs to the nest, even when none are needed. That may be why in rural territories red-tails commonly build a nest and use it only one or two years, then go off and build a new nest elsewhere, when a previous one is still quite usable nearby. We'l have to watch in the next few weeks how strong the stick-bringing behavior plays out this year.

It's still early.

John A. Blakeman