g'day listers,
If I may continue the discussion on breeding and moult, Stephen has made a
couple of points that I am curious to follow up.
(1) "Intensive breeding activity wears out feathers".
Feathers are dead, and so the physiological stress of breeding can have no
effect on them. I cannot see how breeding would increase the rate of decay
from U.V. radiation or bacterial attack. Possibly abrasion may be increased
in sitting birds but I am not convinced that it would be significant. Maybe
lice attack is more serious in incubating and brooding birds (it certainly
is in chooks). I would expect that degree of feather wear more closeley
correlates with age of feather than anything else, but this is just a hunch.
(2) I do not understand the argument that "environmental conditions that
generally favour post-breeding moult in Australian passerines usually
follow conditions that favour good breeding conditions."
Going out on a limb, I can't think of any good reasons why environmental
conditions that favour breeding DIFFER from environmental conditions that
favour moulting. Surely breeeding and moulting are two energy demanding
activities that are largely exclusive of each other and compete for time in
a birds life. Meanwhile, environmetal conditions go through peaks and
troughs that are practically impossible to predict. Perhaps moulting
requires less energy than breeding and so can occur as conditions
deteriorate.
I suppose if birds began breeding as conditions improved, and young fledged
at or just after conditions reached an asymptote then moult could also
begin when conditions were favourable
(3) A minor point is that linking the terminology of moults to the breeding
cycle (ie "post-breeding moult") creates in this instance something of a
circular argument. For instance, sandpipers BREED, MIGRATE, MOULT, MOULT,
MIGRATE and then are ready to breed again. Calling these two moults
post-breeding and pre-breeding respectively is a bit misleading, but that
is what they are most often called. For this reason (and others) Humphrey &
Parkes (1959) proposed a terminology for moults that is based on the cycle
of plumages and moults itself rather than on the seasons, the breeding cycle.
Cheers,
David James
PO BOX 5225
Townsville Mail Centre 4810
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