For those, pre-dominantly northerners, that are interested in koel
plumages. There is a paper in "Corella" that might be of interest: H.J.
De S. Disney. 1992. Ageing, sexing and plumage of the Australian Koel
Eudynamys cyanocephala. Corella 16: 97-103.
A short summary:
Juvenile- largely as illustrated by Slater.
Immature - Generally similar to adult female. The underparts of males may
be in two forms a) throat black with centre buff and black, breast black
with deep buff tips and outer feathers buff or white with brown bars. b)
throat black with centre black with rufous tips, breast deep rufous,
wearing black to white with narrow dark bars beneath the rufous.
Immatures can be sexed easily in the hand on the basis of males having a
black patch on the patagium and shoulder of the wing, that of the female is
spotted. This is apparently only seen when the wing is outstretched.
Moult (this is where it gets interesting) - Young birds may leave the nest
in full juvenile plumage or may moult into immature plumage while still in
the nest with some parts of the body moulting directly into blue-black
adult-type plumage. These changes may start before the wing and tail
feathers have fully emerged from their sheaths. Although the underparts of
young males develop a full immature plumage, the upperparts do not; the
black-blue adult-like feathers start to appear before the immature plumage
Confused? There is apparently a lot of variation in the plumage of young
males from the time they leave the nest. It is also interesting to note
that the nestling period is about 19 days but this would seem to be
influenced by diet. Nestlings raised by figbirds at Pleystowe, Queensland,
apparently took 28 days to fledge while those raised by figbirds in
Brisbane took 19 days. It is suggested that diet, or the amount of food
provided, may well influence the rate at which fledglings moult from
juvenile plumage into immature and adult-type plumage.
Everything you ever wanted to know about young koels but were afraid to
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