birding-aus
At 21:34 22/03/99 +1000, Rohan Clarke wrote:
>birding-aus
>
>Hi all,
>I have no banding experience with drongos (of any description) but it sounds
>to me like these birds are finishing a standard tail moult where the two
>central tail feathers are lost and replaced first followed sequentially by
>each 'pair' of tail feathers until the outer pair are replaced by new
>feathers. Several tail feathers can be growing at anytime so while the
>central few may have reached their full length and stopped growing the outer
>few may not have reached full length yet. Both adults replacing their tails
>and immatures moulting into their first 'adult' tail may have tails similar
>to the birds described by Andrew and Joe so to age them one would best look
>for other characters such as eye colour.
Rohan's comments are spot-on and I was not going to comment, but...
Today in the Museum of Tropical Queensland Jo wieneke and I found a drongo
with the "Ratchet-tailed Treepie" tail. This bird was an adult in its
annual "pre-basic moult" (or post-breeding moult, but doesn't it make sense
to name a moult for the plumage that it introduces rather than for some
relatively unrelated life-history event that it might follow?). This is the
annual moult in which all the feathers are replaced in (just about) all
birds. It had the inner 5 pairs of tail feathers all new fully grown and
shiny, the outer pair partialy grown. Also the 8th primary (3rd from the
outer most) was growing on each wing, the inner ones were fresh and the
outer were old. There were a few scattered contour feathers also moulting,
a few old and worn contour feathers (with metailic spangles on their tips)
amongst the mostly new contour feathers.
2 features allowed the bird to be identified as an adult. Firstly the moult
pattern: when chicks moult into their Juvenile plumage (which by definition
is the first feathered plumage after the down(s)) they moult all feathers
at once. All primaries are growing, all tail feathers are growing. some
finish before others but the pattern is distinct. Thus a moulting juvenile
can have a short tail but not a tail with some long and some short
feathers. Also juveniles can't have old feathers.
The second feature is that juvenile Drongos lack the greenish metalic
spangles on the breast, crown, wing-coverts etc that adults have, and they
look a bit drab by comparison.
Because this bird had both old and new feathers with spangles it was
undergoing at least its second moult. However, It can't be determined
whether the old feathers now being replaced had themselves replaced adult
or juvenile feathers.
David James
PO BOX 5225
Townsville Mail Centre 4810
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