Hi Graeme,
Thanks for the great photo of the two WBSWs at your place. It certainly
shows very nicely the difference in eye colour between adult and juvenile,
so I agree with you entirely that one should just refer to adult scrubwrens
when discussing geographical variation in eye colour.
In my earlier emails, I indicated that blue eyes in birds are a result of
lack of melanin production by melanocytes in the irides. Melanin production
is triggered by Melanin Secreting Hormone (MSH) from the pituitary gland.
Coloration of the feathers and integument is under the influence of the
reproductive hormones (testosterone and oestrogen) and MSH, and high levels
of MSH also helps to increase the secretion of the reproductive hormones.
Circulating levels of testosterone (males) and oestrogen (females) would be
low in juvenile scrubwrens, so you might expect that MSH levels would be low
too, hence the blue eyes. I make the case that scrubwrens who are
physiologically-stressed due to prolonged exposure to extreme environmental
conditions (e.g. salt-loading of their diet in marginal environments) don't
develop the yellow/buff/brown irides when they become adults because of
reduced MSH secretion. I've argued further that one possible reason for
reducing MSH secretion is to suppress secretion of aldosterone from the
adrenal gland so that excess salt can be excreted from the body. Whether
there is any truth to this is anyone's guess, but it would certainly make an
interesting study.
Cheers,
Stephen
Stephen Ambrose
Ryde NSW
-----Original Message-----
From: Graeme Chapman
Sent: Saturday, 26 May 2018 4:51 PM
To: Stephen Ambrose <>
Cc:
Subject: Scrubwrens
Hello Stephen,
Thought you might like to see this one, an adult WBSW with dependent young
at my place - Basin View NSW.
Shows the clear normal yellow eye colour of an east coast bird and a
juvenile.
How to describe the colour in the juvenile is interesting - grey-green?
The point is that when discussing races/places and eye colour we should be
careful to only deal with adults.
I believe that the eye colour of young birds changes gradually to yellow (in
the east) but it may take more than a year.
Cheers
Graeme
<HR>
<BR> Birding-Aus mailing list
<BR>
<BR> To change settings or unsubscribe visit:
<BR> http://birding-aus.org/mailman/listinfo/birding-aus_birding-aus.org
</HR>
|
