FROM ANNIE ROGERS
Some Red-browed, Zebra, Star Finch and Diamond Firetail moult FACTS based
on banding data.
Red-browed Finch and Diamond Firetails in Vic have a pattern of breeding
and moult similar to that of the Grey Fantails I described earlier as do
most Victorian passerines whether they migrate (e.g. Yellow-faced
Honeyeater) disperse (e.g. White-naped Honeyeater) or stay in the same
place all the year (e.g. White-plumed Honeyeater). I would suggest this is
weather related rather than hormonal. Immature Fuscous Honeyeaters from
early broods moult their flight feathers at the same time as adults, late
summer and early autumn, but the late brooders postpone moult until after
breeding the following year (when they are easily recognisable by their
very worn remiges) ? rather than moult in winter? This is based on retrap
data. We suspect many other species do the same, in fact we have never
caught a species that was moulting in winter. Richard Zann has however.
Zebra Finch moult was studied over an eight year period in northern
Victoria by Richard. The results were exceptional for passerines. Primary
moult had an average duration of 229 days for males and 240 days for
females. Limited food, low temperatures and breeding slowed, but did not
stop moult. Birds caring for eggs and young actively replaced remiges.
Birds hatched in autumn postponed the start of primary moult until spring
but adults could start at any time, although less likely in July and
August. Breeding was almost continuous from September to April with some
pairs raising up to SIX broods. It was suggested that the pattern of wing
moult may be related to the opportunistic breeding strategy necessary in an
arid, unpredictable environment and its presence in Victorian birds may be
non-adaptive.
Star Finch. We caught 111 near Camballin in the south Kimberley on the 6th
and 7th of April 1991. The difference between the sexes became obvious to
us after a while and we sexed 54 as male and 25 as female. 13 birds, 7
males, 6 that were not sexed, but none sexed as females had started to
moult their inner primaries; the others had old or very old primaries and
their was no sign of stopped or suspended moult. Only the females had
large brood patches and no young birds were caught, suggesting that females
were still incubating eggs. Three had eggs visible in their abdomens
visible through the bare brood patch area. Not having banded or bird
watched the area before, we did not know whether it was a regular breeding
habitat. What we did know was, that following a particularly long and
?wet? wet, the whole area was under flood water from the Fitzroy river a
few weeks earlier. This happens periodically, but not every year and some
times the wet is ?dry?! So do tropical birds have yet another moult
strategy so far undescribed? The Star Finch would almost certainly do a
complete moult following this breeding attempt ? in winter, not really a
hassle in a tropical area but would this happen in a drier year?
So, is this a case of birds that breed opportunistically developing very
worn primaries and then moulting in the way that Stephen suggests they
should? Without information on what the birds did earlier in the season
there is no way of knowing. The data on moult on all of the other species
mentioned was collected almost on a monthly basis over many years, and to
be able to say anything conclusive about the moult of the Star Finch would
take the same sort of effort. Only then could a physiologist begin to try
to comprehend what caused what. And would it necessarily apply to all of
the tropical passerines?
Stephen, I think much more hard data on the moult strategies of Australian
bush birds is needed before anyone can realistically analyse the
physiological mechanisms involved. While speculation can be interesting it
can also be misleading especially when qualified with ?there is evidence?
that is then not produced.
It will be intriguing to see what patterns emerge in the next few years
with more banders in the tropics and arid regions now routinely recording
moult, and the ongoing examinations of museum specimens by the plumage
handbookers.
Annie Rogers
References
Rogers, K. et al. (1986) Bander?s Aid: A Guide to Ageing and Sexing Bush
Birds.
Zann R. 1984. Slow continuous wing-moult of Zebra Finches Poephila guttata
from southeast Australia. Ibis 127: 1-13.
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