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> From: Stephen Ambrose <>
> Date: Sunday, 17 May 1998 1:15
>
> Let?s examine Annie?s excellent descriptions of Grey and Rufous Fantail
> breeding, moulting and movements:
>
> ?Grey Fantails spend about 9 to 10 months of the year in southern Vic
(some
> don't leave at all). Grey Fantails are far more widespread in Vic than
> Rufous Fantails but where they overlap they share the same habitat. Grey
> Fantails breed from early Sep to late Dec, possibly later. Grey Fantails
> moult everything (not just primaries) from Jan to early April. Most
leave
> at the end of May, but a few remain all year - probably immatures. Grey
> Fantails almost certainly raise more than one brood a year.?
>
> This is a clear example of moulting being tied to breeding.
NO STEPHEN !!
This is clearly an example of moulting decoupled from breeding. The point
that Annie made was that in two closely related species the timing of moult
is different despite the fact that they've just bred. Lets step back..
08/05 Harvey Perkins, having pre-empted evolution with two sets of wing
shapes mused "Also if body feathers can moult more than once each year
there is presumably not a lot stopping wing feathers doing the same".
08/05 Stephen replies (in haste) "There is some evidence that a few
Australian arid zone birds may occasionally moult their wing feathers more
than once a year".
08/05 The big question from David James "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?".
Stephen takes the position that moult and breeding are tightly tied and
that breeding is so wearing to feathers that moult will inevitably be
required at the end of it. Both of these positions were challenged. Let me
summarise and extend the arguments (please do not be offended if I've
borrowed your points without acknowledgment - just be flattered that
they're being put to good use).
Feather Wear.
Take a species in the water privileged SE of Australia that has two broods
in a season. It does not moult in between. It moults after the breeding
season. Take a species in the arid zone that raises one brood in spring,
then moults, then in the presence of good rain breeds again. At the end of
the year both have raised two broods, sustained the same breeding related
feather wear and moulted once. Why must the arid zone species now moult
again?
Arctic breeding waders' feathers are good enough to fly to Australia after
breeding.
The Breeding/Moulting Nexus
In a good year a successful adult bird will breed and it will moult. Both
are extremely energy hungry activities and there are good reasons for them
not to happen simultaneously and mostly they don't. It is highly likely
that the levels of sex hormones found during breeding inhibit moulting.
That is quite different from saying that moulting is triggered by a fall in
sex hormone levels.
If there was a strict link between breeding and moulting then one would
inevitably follow the other. In fact, beyond being prohibited during
breeding (mostly), moulting shows considerable variation. AND MANY BIRDS
WILL MOULT NUMEROUS TIMES BEFORE THEY EVER GET THE OPPORTUNITY TO BREED.
If two events occur in a cycle it may appear that they are linked but
remember New Years Day does not cause Mother's Day or vice versa.
Correlation ain't causation.
Conclusion - Feathers must be moulted because of wear not breeding.
Now the real answer to the big question "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?".
Is a big don't know. The evidence is absent. It simply is not good enough
to argue from first principles that the hormonal mechanism demands a second
moult. Such evidence as we have seen, put forward by the Rogersii, supports
the contrary argument, Yellow-tufted and Fuscous Honey-eaters bred
opportunistically and did not moult subsequently (Danny 11/5). Grey and
Rufous Fantails behave quite differently after breeding (Annie 15/5).
Numerous exceptions to the rule (Kenny 13/5). In the beginning Stephen said
there was evidence - lets see it!
Robert Berry.
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