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Hi David,
See my other message of
yesterday. I'm very pleased that - as you say "Well, that's a first for
me!". That is exactly why I put it in the text (one of the referees
sugested I leave that line out). If someone demonstrates it to be true or indeed
not true, I will be very glad that I was the first (perhaps) to have suggested
it. The vast majority of my GBS report is straightforward presentation of data.
That particular line was one of the few items of conjecture or suggestion. It is
after all, a better suggestion than any other, as to why these birds migrate
north - south rather than up - down, as nearly all the other honeyeaters that
inhabit this region do.
You wrote that "The knob, and the associated depressions
either side of the knob, are also wonderful collectors of pollen ensuring cross
pollination as birds move between plants." That may be true but that is an
advantage to the plants but hardly of any benefit for the birds. The birds
aren't going to evolve something to benefit the plants, unless it has been of
historical adaptive benefit to the birds that started to develop that feature.
Absence of feathers on parts of a bird where they are not needed is an advantage
to the bird, as it doesn't need the energy to grow or maintain the feathers.
Just as birds that live in places where they don't need to fly, typically evolve
to become flightless. However a bird that happens to be bald, is likely to have
a hard time surviving the cold winters here, hence they migrate
north.
Philip
-----Original Message-----
From:
<>
To:
<>
Date:
Thursday, 19 September 2002 9:15
Subject: [BIRDING-AUS] Noisy
Friarbird - WHY BARE HEADS AND BILL KNOBS?
"Philip
Veerman in his "Canberra Birds: a report on the first 18 years of
the garden bird survey". He suggests they have to leave Canberra
for the
winter because of their lack of head feathers -
exposing them
to cold."
Well, that's a first for me!
I'm sure there are
more practical reasons for leaving honeyeaters
Canberra, probably the
same reason most Yellow-faced Honeyeaters leave the
high country and
migrate north.
In regards lack of head feathers, I suggest it's all
about feeding in
blossom with high volumes of nectar. The knob,
and the associated
depressions either side of the knob, are also
wonderful collectors of
pollen ensuring cross pollination as birds move
between plants.
Ten or so years ago I was collecting pollen samples
from birds captured in
coastal heathland on the NSW north coast.
Pollen collected in and around
the nostrils of most birds and over the
head an chin feathers but
friarbirds would have a virtual reservoir of
yellow pollen at the base of
their knob.
Hope that
helps.
David Geering
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