Greetings,
From the Dr Karl article, " Fourth, the manufacture of the train is
controlled by oestrogen (female) hormones, which is very unusual for a
display ornament that supposedly affects mating success. Testosterone (male)
hormones are far more common in this arena."
I was under the impression that oestrogen is quite commonly the controlling
hormone in the production of breeding plumage in birds where the eclipse
plumage and female plumage are the same or similar. Would some one clear
that up for me?
Regards,
Alan
--------------------------------------------------
From: "John Tongue" <>
Sent: Friday, February 19, 2010 6:00 AM
To: "Peter Shute" <>
Cc: "'Birding Aus'" <>
Subject: Peacock coutship
Not sure how they prove all these claims in Dr. Karl's thesis, nor what
they "mean"
BUT......
An intrigueing thing I've noticed about a Peacock's display, ever since we
had Peafowl when I was a kid, is that once the male erects his 'tail' and
begins his shimmering display, is that he turns his back on the object of
his desire. She mostly gets to see the plain feathers around his
backside!! I wonder what criteria she is really using to make her
choice??
John Tongue
Ulverstone, Tas.
On 19/02/2010, at 6:39 AM, Peter Shute wrote:
What Dr Karl said is here:
http://www.abc.net.au/science/articles/2008/06/17/2277297.htm
"Just recently, my primary school daughter, little Lola, did a school
project on the peacock.
She made a magnificent model, and wrote an essay that included the
widely-held belief that the purpose of the splendid plumage of the male
(the peacock) is to attract the female (the peahen).
But this simple "fact" is actually a puzzle, and is almost certainly
wrong.
Now the first thing to realize is that the peacock's "tail" is not
actually his tail.
His real tail feathers are quite small and nondescript. The big showy
plumage comes from feathers which are on his back, not his tail. To avoid
confusion, the bird scientists call it a "train".
The standard belief is that the peacock does his magnificent feather
display specifically to attract the female peahen.
The peacock can raise the long feathers of the train into a glorious
semicircle, about two metres across (not bad for a bird only about a
metre long).
Each brilliant metallic-green feather carries an iridescent eye. The
feathers keep growing during the autumn and winter, and molt once each
year in the summer.
The story goes that when the peacock spies a potential mate, he erects
the feathers in his train into a fan.
He then draws the fan forward and wraps himself in it, and then sends
ripples running through the feathers.
He then draws the fan further forward, and quivers it so violently that
it takes on a shimmering appearance while the feathers make a rattling
sound. This part of the courtship is called the ecstasy.
He will then manipulate the muscles at the bottom of each feather to
change the loudness of the sound, and does this about twice each second.
This is called a shiver, and a peacock keen to impress a peahen can
generate up to 20 bouts of shivering, with each bout lasting up to six
minutes, or more.
The display is spectacular, and it's definitely done for the benefit of
the female peahen. But, she is not automatically won over.
Instead, she will normally perform one of three behaviours: ignore it and
pass on by; passively accept the display; or actively solicit the
display.
On the surface, this seems like a classic case of sexual advertisement by
the peacock. But over the years, there have been pieces of data that
don't fit in with this simple picture.
First, the peacock often displays his train after the female has started
the courtship routine, not before.
If the Big Display is his advertisement as to how good it can get, surely
he should do a display before the female starts the courtship?
Second, over the years, there has been conflicting evidence both for and
against the link between the train display and mating success by the
male. There is not a general consensus.
And as a part of this conflict, there are still continuing arguments
about what are the most successful aspects of the train.
Would it be its length, or the diameter of the eyes in the feathers, or
the number of eyes per square metre, or the frequency of the shiver, or
the symmetry of the train, and so on? The question is far from resolved.
Fourth, the manufacture of the train is controlled by oestrogen (female)
hormones, which is very unusual for a display ornament that supposedly
affects mating success.
Testosterone (male) hormones are far more common in this arena.
Fifth, there is actually not that much difference between the trains of
peacocks across different populations of the birds. So, to a potential
mate, one peacock's plumage is as good as another's.
And finally, the quality of the train itself does not accurately reflect
the genetic and health conditions of the peacock — thus making it a false
sexual advertisement.
So that leaves us with the increasingly probable position that the
glorious train and display of the peacock is an advertisement that once
might have had significance, but is now obsolete.
In other words, the peahen is really interested in other aspects of the
peacock (perhaps his stimulating conversation) but even to qualify in the
mating stakes, he needs a pretty train.
So why does he still have this magnificent spread of plumage? Maybe, like
most males, he's his own biggest fan."
Peter Shute
________________________________________
From:
On Behalf Of Philip Veerman
Sent: Thursday, 18 February 2010 11:51 PM
To: 'Nathan'
Cc: 'Birding Aus'
Subject: RE: [Birding-Aus] Peacock coutship
Sounds like someone has got their wires crossed. That sounds
nonsensical. For one thing males court the female, not the other way
around. The female is the one who decides. Of course everything in
evolution is an accident but it is also driven by a process, so it is
not without reason. The train of a male peacock is so elaborate and the
behaviour that goes with it is so extreme that it is absurd to suggest
it is not a huge advantage to the males who grow the biggest brightest
trains. So in that way it is not an accident, it is surely driven by
female choice over the generations (it is not actually a tail, it is the
overgrown rump feathers).
Philip
-----Original Message-----
From:
On Behalf Of Nathan
Sent: Wednesday, 17 February 2010 8:55 AM
To: birding-aus
Subject: [Birding-Aus] Peacock coutship
I was listening to an ol podcast of Dr Karl yesterday and he said that
the female peafowl decided whether to cout a male before she even sees
the males tail and that the tail was an 'Evolutionary Accident' I don't
doubt this as fact but I am wondering how on earth you would test that?
~Thanks
~Nathan Ruser
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