Geoffrey,
Good that you
actually mentioned ?double-brooding? in the Pied Currawong (PC). This was a cue
to think a bit more about this issue, and even better, COG members may now pay
closer attention to their local PC, irrespective of whether they like the
species or not .
What you
describe would seem to be most likely a replacement brood after
failure of the first brood at a relative early nestling stage. Species that are
able to initiate a replacement brood after failure of the first brood may do so
only if the loss of the first one happened at a fairly early phase of the
nesting cycle (eggs or small young lost). If young are older and closer to
fledging at the time of brood loss, it may already be too late in the breeding
season to start a new clutch. What may happen in the urban Currawong though is
that with good food supplies available, they may be able to initiate re-nesting
even when the loss of the young of the first brood occurred rather late, hence
it may be possible to see first nestlings as late as early January as you have
mentioned.
Another option
birds have to manage two broods within a limited breeding season, is to have
overlapping broods. That means the second brood is initiated before the young of
the first brood are independent. As a rule one partner will mainly care for the
young of the first brood until independence from the point the 2nd
brood is started, while the other focuses more on the new nest. A fine local
example for this behaviour is the Leaden Flycatcher.
If PCs raise
several young, it is not uncommon that each partner looks mainly after one set
of young, rather than that both
male and female distribute their attention equally among all young (this
behaviour can make it at times difficult to determine the number of fledged
young in a brood: you see an adult
with a begging young, while their may be an extra 2 young fed by the other adult, however the latter
young may be quiet at the time when you noticed the former young!). Hence, one
of the pre-conditions for overlapping broods ? the ability of only one partner
to complete the raising of the first brood to independence, may be met in the
PC. However, the proof for double-brooding (sequential or overlapping) for the
Canberra PCs is still outstanding!
Also many thanks
to COG members who have responded privately to my earlier message on Currawong
and King Parrot roosting behaviour.
Michael
Lenz
