At 11:24 8/05/98 +1000, Stephen Ambrose wrote:
>If an Australian arid-zone bird breeds in early spring (as a seasonal
>breeder), moults in late spring/early summer at the conclusion of breeding,
>and then summer cyclonic rains falling in late summer stimulates further
>breeding, then it's likely that these birds will moult again in autumn/early
>winter. Thus wing moult would occur more than once in a 12-month period.
>
>The question is, can the same individuals breed both seasonally and
>opportunistically in the same year, or do some breed seasonally and others
>in the same population breed opportunistically?
>
A few brief points:
Is there evidence that an arid-zone bird that breeds opportunistically for
the second time in a year is likely to undergo a second complete moult
after completing breeding. This is an example of a sub-annual cycle
(completing all the "annual" activities, namely breeding, moulting,
migrating, in less tha a year). (They would not be migrating anywhere).
Moults have been linked by name to the breeding cycle (ie post-breeding
moults) which is unfortunate. Birds do not moult because they breed, they
moult primarily because their feathers wear out, and secondarily to change
appearance. My tenuous understanding is that when the cycle is sub-annual
and or irregular the synchronisation between breeding and moulting breaks
down.
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?
David James
PO BOX 5225
Townsville Mail Centre 4810
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