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[T40cfr403]

Thanks jf!  Good info, as always.

Read a few other posts in this thread and your "Flap, Glide, Soar" observations were stunning.  What a life-changing event to witness.  Jealous.

I was also impressed by the information that nestlings imprint on prey.  Watching Dad bring in a dizzying array of prey those first few days after hatch has even more meaning now.  I thought his sole purpose was to provide a wide variety of protein that was easily digestible.  But now I realize it was also a teaching opportunity to show the eaglets appropriate prey.  Genius.  Almost too much to comprehend at times.

[shaggydog1]

Another big thanks to you, jf, for this information.  You write so well and it's so easy to read and comprehend.  Not at all the stodgy, documentary style of many writers!!! Thank you!!!

[jfrancl]

You're welcome T40 and Shaggy! 

It's great that so many of us are interested in learning more and more!!   

[myschatzi]

Another big thanks to you, jf, for this information.  You write so well and it's so easy to read and comprehend.  Not at all the stodgy, documentary style of many writers!!! Thank you!!!

Agreed Shaggy... It brought tears to my eyes just reading about our E's milstones..  I will continue to read more.  Info is very informative, I'm still learning!! 

Thank You, jf for the link   

[T40cfr403]

I spent a couple of hours watching the autorecords of the close-ups on 4/24/15 and was particularly interested in D23.  My main problem is I don't know the biology of feather growth, so what I thought I saw could be way off base.  It seemed to me when D23 was preening the thermal down, s/he was just breaking up clumps of the down.  It reminded me of humans nibbling on an ear of corn (not that corn!) because its beak wasn't pulling on anything and the beak always came away clean, with no down attached.

So I was thinking maybe the purpose of that action of quick, short strokes over a large area might be useful in simply making way for the remaining natal down to come to the surface (here's where my feather education fails me).  The preening nibbles might be triggered by them feeling pin feathers starting to grow below the surface of the thermal down.

My theory doesn't explain why natal down pops up through the thermal down on the head almost overnight with no preening possible and in such even patterns, but maybe head feathers/follicles are different from those on the rest of the body?

Or, again with the lack of knowledge (!), but they keep the thermal down, right?  So maybe D23 really was preening the thermal down because it's also growing and morphing into those soft, white, tiny, downy feathers?  Those white down feathers just don't grow with the same type of sheath the pin feathers have, right?  Or maybe there is some type of protective coating on the thermal down that needs to be nibbled away?  Oh, I've dug myself a deep hole and sorely need a textbook! 

[jfrancl]

Thanks for your post T40.  I didn't see what you were referring to but I'll give this a shot.

 Down feathers normally lack a rachis and do not form a vane.  Contour feathers will push out the natal down ahead of it and second down has no tracts as the natal down does have.  The second down follicles aren't evenly distributed but are randomly spaced amongst the tracts of the contour feathers.  So the second down, replaced in molting, is a permanent underlayer of the down throughout the bird's life.  D23 is 24 days old, and at about 3 weeks old, eaglets are largely covered with their second coat of down.  By day 18-22 very little natal down is visible, except on the top of the head.

Down feathers in adult birds is called Definitive Down and vary from thick to restricted distributions.

Hope this helps.

[T40cfr403]

ty jf