Just to add picture, male and female Tasmanian Scrub- wren April 2018.
Interesting discussion.
I am interested if anyone has good reference to the physiology / biochemistry
etc on eye colour changes. Is it just age or are there other factors? There has
been some discussion with Brown Thornbills ability to change colour seasonally
or even acute stress. I do not have references. Thanks
Geoff Shannon
On 27/04/2018, 4:04 PM, "Birding-Aus on behalf of Graeme Chapman"
< on behalf of
> wrote:
Hello Mike,
Thank you so much for replying to my request. I'm attaching my K I image
that should have been attached to the original but was removed somehow in
birding-aus.
I'll agree, your bird's eye has a greenish tinge but it is also rather dark
and dull and in my opinion, a probable young bird.
I've been looking at the books on this one and what a can of worms! In
HANZAB you can take your pick in the text on soft parts and in the plate, it
shows maculatus with a yellow eye, which is wrong. The new CSIRO "guide" opts
out altogether on iris colour in the text and the plates are really too small
be of any use on this subject. What a pity this book wasn't published as a
concise handbook in A4 format. They obviously have all the information but it
has been compromised by shoehorning into too small a space.
What I am fairly sure about is that age is a factor here as it is with many
of our small birds - we know so little because so few of our birds have been
studied in detail.
I have a wide range of pics of this species and I'm attaching a few examples
The first two are Brown Scrubwrens from Tasmania. The first one is an adult
male at the nest - I would describe that iris simply as yellow.
The second bird at the same nest I always assumed to be a female (on
plumage) but it has an olive coloured eye - such dull colours are usually
characteristic of younger birds and it is much more likely to be a helper than
the adult female, or if it is the female it is a younger bird. I don't expect
the sexes to have different coloured eyes as adults. This eye colour reminds me
of your K I bird.
The next pic is what I regard as a classic frontalis and I would describe
that as pale yellow - virtually all east coast birds are like this, maybe a bit
darker as you go north.
The last is the old "Buff-breasted Scrubwren" of the 1926 Checklist from
northern NSW, slightly darker yellow.
I guess what I am on about here is the difference between "Spotted" and
"unspotted" birds. All the Spotted ones I've seen have the pale blue eyes,
which gives them a totally different (to me) look.
So. how long do they take to become adult ( by eye colour )? I'd say at
least two years.
I guess I'm on the same bandwagon as my recent comments on Eastern
Whipbirds. Most of the books get that one wrong and show adults with brown
eyes, whereas in fact they are cream. How long it takes nobody knows but it's
likely to be similar to the Grey-crowned Babbler which is four years.
What really started this interest was the years I spent with Ian Rowley
studying corvids and choughs, both of which can be aged by eye colour, a very
handy indicator when you are looking at life history. We worked with birds we
banded in the nest, so we KNEW how old they were. Getting to the Australian
Raven's nests was interesting, I can't even lift a rope ladder any more, let
alone climb one.
Cheers
Graeme
Spotted Scrubwren from Kangaroo Island - eyes pale blue
>
Brown Scrubwren male at nest, eyes yellow. I assume this is an adult.
Brown Scrubwren at nest, probable immature, eyes olive.
White-browed Scrubwren, Gloucester NSW. eyes pale yellow. Virtually all
east cost birds are like this,
White-browed Scrubwren. Tooloom northern NSW subsp.laevigaster - eyes
yellow
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