Dear Harvey,
There is some evidence that a few Australian arid-zone birds may
occasionally moult their wing feathers more than once a year. Australian
bird species are essentially seasonal breeders, even in the semi-arid and
arid zone. However, arid and semi-arid zone species can also breed
opportunistically outside the usual breeding season after heavy rainfall.
Feathers (especially wing primaries and secondaries) are usually very worn
after a breeding attempt and so are moulted sequentially and new ones grown
once breeding is completed.
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?
Written in haste ...
Stephen
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