At 04:54 PM 5/8/98 +1000, David James wrote:
>A few brief points:
>Moult, migration and breeding are the three potential major demands on
>energy that a bird faces in a cycle. Typically these occur sequentially
>rather than concurrently, and one may be delayed while another is underway
>(suspension of moult during breeding or migration, delay of migration while
>moult completing). In an opportunistic system where breeding opportunities
>could arise at any moment, would there be much advantage in committing to a
>moult straight after breeding, irrespective of the condition of your
feathers?
Hi David,
In my experience, the OPPORTUNISTIC breeding activities of Australian
passerines are very intensive if environmental conditions are good. In
fact, a pair may breed more than once if the conditions are very good and
prolonged. This was recorded by Peter Congreve (former warden of Eyre Bird
Observatory) and myself at Eyre in the early 1980s, for a range of bird
species.
Richard Zann of La Trobe University has also recorded multiple breeding
attempts of Zebra Finches after heavy rains in the arid zone.
Such breeding activity really does have a very wearing effect on flight
feathers, and I don't think birds have much of a choice but to moult them
and grow new ones. I remember being on Barrow Island (a desert island off
the north-west coast of WA) in February 1993, a couple of months after
cyclonic rains had passed over the island. Some Spinifexbirds had completed
breeding by then and had shed all their secondaries concurrently, and their
primaries were being moulted sequentially. So these birds, at least, were
going through a complete moult.
When our research group had visited Barrow Island in July 1992, some
Spinifexbirds were breeding, and I believe this was the usual SEASONAL
breeding response.
Unfortunately, we did not have enough information from these two visits to
know if the same individuals bred in both July 1992 and February 1993.
I believe that arid and semi-arid zone birds breed OPPORTUNISTICALLY when
environmental conditions are exceptionally good and resources are
plentiful. Therefore, they undergo a complete moult at the end of breeding
if there are still adequate resources to enable them to do this.
Conversely, I have seen birds in the semi-arid zone that undergo only a
partial wing moult after a poor SEASONAL breeding period, presumably
because there were inadequate resources for the growth of new feathers.
Trevor Quested wrote:
"Do White winged Trillers have something unusual about their moult? I seem
to remember Arnold McGill telling something about them & I've forgotten".
Trevor, I do recall Arnold saying something about unusual moulting patterns
in White-winged Trillers. However, I too, have forgotten what it was, or
the source of his paper. Perhaps some other Birding Ausser can help out.
Cheers,
Stephen
************************************************************
Dr Stephen Ambrose
Research Manager
Birds Australia (Royal Australasian Ornithologists Union)
Australian Bird Research Centre
415 Riversdale Road,
Hawthorn East,
VIC 3123.
Tel: +61 3 9882 2622
Fax: +61 3 9882 2677
Email:
1997 Australian Bird Research Directory is on Birds Australia's
home page: <http://www.vicnet.net.au/~birdsaus>.
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