At 11:30 PM 19/04/99 +1000, van Roekel wrote:
I
>would greatly appreciate some clarification of when a bird is juvenile and
>when immature or whether it can be both at once.
Hi,
Juvenile is now very widely accepted as the name of the first pennaceous
plumage of a bird - i.e. the first set of contour (real) feathers grown at
fledging.
Immature does not seem to be so rigourously defined. Some people persist in
applying the term to any non-adult plumage. Most recent serious handbooks
have restricted the term to plumages which are held between the period when
the juvenile plumage has been moulted, and before the adult plumage has been
attained. By this definition, a bird can't be both juvenile and immature at
the same time (although when it is moulting from juvenile to immature
plumage it has bits of both plumages). Some species of birds moult directly
from juvenile to adult plumage (e.g. most penguins) and thus don't have an
immature plumage; in other species (e.g. most gulls) there can be several
immature plumages.
As for Hooded Plovers: I think you saw a juvenile. In brief summary (fuller
details are in HANZAB): Hoodies fledge in a plumage that is paler-headed
than the adult. Initially most of the head is dark greyish brown mottled to
by pale brown to whitish feather-tips. With wear these tips are lost
(resulting in a fairly uniform looking greyish brown head); with extreme
wear the ground-colour also fades, becoming paler and greyer. The
illustrations in both Slater and in Pizzey & Knight are both accurate
depections of juveniles, but they show birds at different stages of wear.
Neither is strictly speaking an immature. Hooded Plovers do moult into an
immature plumage in autumn. It is extremely similar to adult but in the hand
can usually be distinguished because they retain juvenile primaries
(differing from adult primaries only in wear)and sometimes some scattered
juvenile body-feathers.
Both Slater and Pizzey & Knight's field guide give a correct definition of
juvenile in their introductions and glossaries. But for some reason, Pizzey
& Knight have not used the definition in the plates or text. Almost every
juvenile illustrated in the book is incorrectly labelled immature;
occasionally they have labelled an illustration 'juvenile' instead of
'immature' but I can see no consistency in their approach at all. I have to
agree, it is VERY confusing.
Danny Rogers.
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