Hi all,
Yet more on moult. The moult discussion is becoming rife with assumptions
that are not being justified. The thread of the discussion is diverse, so I
apologise if this comment jumps a bit.
Stephen Ambrose continues to assert that "intensive breeding" causes
extreme feather wear. I have made an invitation for evidence supporting
this assertion to be presented, but so far I have seen none. To help things
along I provided some purley speculative reasons why breeding may
significantly increase wear. Now I will provide some speculation as to why
it may not:
UV radiation is the most significant cause of feather deterioration and
breeding birds spend significantly more time in the shade (hollow nests,
enclosed nests, nests in shady trees) so wear is slowed while breeding.
Wear of flight feathers is proportional to how much time the wing is open
and the coverts are not protecting the feathers. Breeding birds spend less
time with wings open.
Food is more available when conditions favour breeding and breeding birds
therefore spend less time foraging even though they may have more mouths to
feed.
If you look at a large sample of birds you will not find convincing
evidence that fearthers are unusually worn immediately after the breeding
season. At least, in the thousands of museum specimens of about 100 species
(mostly non-passerines) that I have examined for moult I have not seen such
a phenomena. Therefore, I propose the following null hypothesis that:
wear of feathers is directly proportional to age of the feathers.
Can anyone knock this over with COMPELLING evidence?
The following are a range of examples of moult strategies in birds.
Female Golden Plovers (Pluvialis sp.) have a supplemental moult of the
breast that occurs during incubation, then they migrate, then they have a
complete moult.
In Brown Goshawk, females do c. 90% of incubating and brooding and males do
90% of feeding the family. Females moult their primaries during nesting,
some beginning at the time of laying, some at about the time of hatching,
some even later. Males moult after young have fledged.
Female Cassowaries mate, lay eggs, and dissapear. Males incubate, brood and
care for the young for about a year. Button Quails are similar but males
and females are not thought to moult at diferent times. Bowerbirds are the
opposite, but I don't know their moult strategies.
Species that moult in staffelmausers (slow continuous moults, sometimes
termed wave moults) moult slowly and continuously all their lives with no
obvious start and end points. What they do is suspend moult when resources
are not available or when they are being channelled elsewhere. Species in
this group include albatross, frigatebirds, eagles, frogmouths, megapodes,
Tyto owls, Osprey, and a host of other, mostly large birds.
Some species have distinct moulting seasons in southern Australia and
varyiable season in northern Australia. Black Kite is one that comes to
mind. May be true of Collared Sparrowhawk.
South Polar Skuas breed, then leave the ice and migrate to the Northern
Hemisphere. They moult in the NH and moult continues during the s.
migration. Although they couple moult and migration they have one of the
quickest complete moults of a bird of their size and one of the longest
migrations of any animal.
I could go on, but the point is this. Birds do not have moult stategies
simply because they breed. They do not have moult strategies simply because
moult increases feather wear. They definately do not have moult stategies
because the have elevated thyroxin levels. BIRDS MOULT TO REPLACE THEIR
FEATHERS AS FREQUENTLY AS NECCESAARY TO MAINTAIN THE FUNCTIONS OF THE
PLUMAGE (insulation, protection, flight, communication, camoflage,...) AND
NOT MORE OFTEN THAN NECESSARY. To acheive this, and breed, and migrate, and
forage, and play, and ... they have evolved complicated strategies that are
not at all well accounted for by physiologists. In the above examples
breeding is always there, not because moult is linked to breeding but
because they are both part of the same life cycle. There is just no
universal rule that moult follows breeding.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>
Peter Woodford said that:
>Lets step back and consider this in evolutionary terms [I thought I was].
>Breeding, the transfer of genes to the next generation is the most
important >thing a bird or other animal can do. The timing of breeding has
evolved to
>maximise the chances of survival of the young, so the most critical phase
>in the cycle will have evolved to coincide with the time of maximal
>resources...
>I'd agree that breeding and moulting are "two energy
>demanding activities" but I'd suggest that feeding the young is more energy
>demanding than moult, and also more "important". Thus moult can be put off
>to a time when resources are a little less abundant>.
To claim that breeding is the most important part of the life-cycle is
surprising to me. More important, than breathing? drinking?, eating?
maintaining condition? avoiding predation or accidental death? A failure of
any one of these will prevent "gene transfer". If passing on genes was only
about breeding then why would animals do anything else? I cannot agree that
bredding is "more important" than moulting. All birds moult. It must be
important, it is never left out. I will agree that breeding MIGHT be more
energy demanding than moult, therefore "more critical" and thus have SOME
priority in resource allocation trade-offs. But where is the EVIDENCE of
this. It is common for birds to abandon breeding and then moult. Maybe
they ONLY abandon breeding when survival of the young is unlikely. Maybe
they ALSO abandon when survival of the young would risk the survival of the
adult (through unrecoverable loss of condition).
If moult occurs at the time when resources are less favourable, then please
explain this. Silver Gulls in victoria are divided into two parrapatric
populations. One breeds in summer and the other breeds in winter. One
undergoes pre-basic moult when the other is breeding.
>>>>>>>>>>>>>>>>>>>>>>>>>>>
Ken and Annie Rogers asked for an explaination of "intensive breeding"
which was then defined by Stephen as a mass breeding episode. Thus,
"intensive breeding" occurs in POPULATIONS. Meanwhile, intensive feather
wear occurs in INDIVIDUALS. The term intensive breeding has been used in
this discussion to imply a period of greater demand than usual for
individuals that places greater wear on feathers. Pull the other one.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
The term "complete body moult" as used by Stephen is an oxymoron (in the
non theatrical sense of the word) Complete moult refers to a moult of all
feathers. Body moult refers to a partial moult of body feathers.
>>>>>>>>>>>>>>>>>>>>
Some of the dubious assumptions in this discussion have stemmed from
entrenched misleading terminology of moults that links them to the breeding
cycle (i.e post-breeding moult, or post-nuptual moult). I will elaborate on
this in a separte posting.
So please, post your EVIDENCE. I am waiting to be compelled.
Cheers,
David James
PO BOX 5225
Townsville Mail Centre 4810
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