Everybody with an interest in moult knows that the most common pattern,
certainly for passerines, is for them to moult after breeding. This
correlation does not establish that the cessation of breeding and the start
of moult are causally related. There must be one most common pattern
whatever the processes involved. Frequency alone would be a poor basis for
imputing causality because of the failure the theory to explain the many
exceptions. Stephen may have erred in relation to Annie?s Grey Fantail
example. She reports that moult follows breeding in this species. This
empirical fact may exclude some theories but gives preferential support to
none. The notion of ?moult being tied to breeding? is one of several
options.
Stephen must also be challenged on his assertion that feather wear
(abrasion) is particularly severe during breeding. Essentially, he is
saying that birds? primaries are abraded more if they have had breeding
attempts than they would be if they hadn?t. Where is the evidence for
this? I have been involved in banding thousands of birds over the last 18
years, mostly in Victoria. My very clear recollection is that, in January,
roughly at the end of breeding and the start of moult, birds? primaries are
not particularly badly abraded (unnoticeably so in species which nest in
confined spaces - e.g. pardalotes, swallows, bee-eaters), although clearly
recognisable as old feathers by their colour and sheen. A couple of months
later the outer primaries, generally the last to be moulted, show more,
sometimes much more, substantial signs of wear. This is presumably due to
prolonged exposure to sunlight in the hottest months of the year and having
had to do more work by flying around compensating for missing or not fully
grown feathers in the wing. As the feathers get older, they get weaker and
more likely to be damaged by abrasion. I very much suspect that, for most
species, breeding activity generally adds little to the feather wear that
birds would sustain in its absence.
Ken Rogers
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