Thanks everybody – I learned something today!
Bill
—–Original Message—–
From: brian fleming
Sent: Wednesday, February 24, 2016 5:03 PM
To: birding-aus@birding-aus.org
Subject: Re: [Birding-Aus] Fw: Kookaburra eyes
Dear Bill,
This is a splendid pair of photos, good enough for any text-book,
showing the third eyelid or nictitating membrane. This is present in
all birds and some mammals (not humans, though we have a vestige in the
inner corner of the eye). This membrane covers the eye as a protection
in situations where injury is possible – such as dealing with prey or
when feeding young. It probably also cleans the cornea. I don’t know
if it covers the eye under-water in diving birds. I am sure the bird
can see through it.
Some people discard photos where it shows, because the eye doesn’t
‘look right’. But it is a normal function and not a deformity.
Anthea Fleming
On 24/02/2016 3:08 PM, Bill Stent wrote:
> I was wandering around Banyule Swamp this morning when I found a
> Kookaburra.
>
> Taking some photos I noticed that when the bird’s head was turned at a
> particular angle the eyes looked clouded, but on a different angle they
> appeared clear (see attached photos).
>
> Does anyone know what this is? Is it an optical thing, related to the
> efficiency of the eyes, or something else?
>
> Bill
>
>
>
>
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