I found the book "The Handicap Principle" by Amotz and Avishag Zahavi
interesting and thought-provoking. Their basic tenet is that for animal
signals to be effective - to be convincing to the receiver - they must
impose a cost on the signaller.
I'm not sure that I agree with all their conclusions, but their theory on
mate selection is spot on when applied to lyrebirds. I'll come to that
shortly, but first let me quote the Zahavis on pelicans. Something I was
not aware of. They write:
"White pelicans, both male and female, grow fleshy bumps between their
eyes when they are ready to breed. The bump interferes with the pelican's
ability to see the area around the tip of its' bill. In order to catch
prey, a pelican with a bump has to remember where it last saw its prey and
project the prey's likely movements. An inexperienced or inept pelican
would not be able to do so. A pelican that can fish and maintain itself in
spite of the handicap of its bump is reliably indicating its expertise in
fishing. Later, when the pelicans have to feed their brood of four or five
demanding young, the bump shrinks and they are able again to hunt more
efficiently."
(Do Australian pelicans grow such 'nuptial' bumps, I wonder.) The authors
continue:
"Singing can also demonstrate the ability to provide. The time invested
in singing cannot be used for foraging. A courting male who handicaps
himself by singing continuously provides evidence that he needs less time to
forage, either because he is very efficient or because his territory is very
rich. Wilhelm and his colleagues studied the effect of supplementary
feeding on the singing of yellow-bellied sunbirds. They found that those
who were not given insects did not sing, while those who received insects
and sugar water sang often and at length. Time spent in sentinel activity,
or in dancing displays, can also indicate expertise in finding food,
especially when the "waste" of time comes early in the morning after a long,
cold night without food."
During the breeding season, male lyrebirds sing and dance at length before
feeding each day - as soon as there is enough light for safety on the ground
- and this is indeed "after a long cold night", for lyrebirds breed in
winter. And especially with Superbs towards the southern limits of their
range, the nights are long and cold.
It has been suggested that lyrebird mimicry enables a male to develop a more
extensive repertoire of sounds to impress females but it is the total amount
of song produced by a male and not the variety of sounds that is almost
certainly the basis of female choice of mate.
Syd Curtis
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