It's seems a slow day on Tweeters, so I suppose this one
more note on "juvenal" vs. "juvenile" won't clog up the
list too much.

For the usage "juvenal" plumage, Martin Muller points to
the authority of the house style defined in the Glossary for Birds
of North America Author Guidelines, the style sheet that the
editors sent to their authors for the sake of consistency:

"Juvenal plumage: The first generation of true (pennaceous)
contour feathers. The feathers are usually less closely-knit,
and differently colored than those which will follow. Acquired
by the Prejuvenal molt (i.e.,replacement of natal down in species
which have a downy plumage) and _usually_ lost by the First Prebasic
molt (but there are exceptions). Do not confuse with juvenile,
a general term for a young bird that has not reached sexual maturity."

On the other hand, I've just pulled out a copy of _National
Geographic Society's Field Guide to the Birds of North America_,
whose editors aver that "[t]he first coat of true feathers, acquired
before the bird leaves the nest, is called the _juvenile_ plumage."

So take your pick between duelling authorities.

--cheers, Jim Lyles, Tacoma