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
>
>
>
>
Birding-Aus mailing list
>
Birding-Aus@birding-aus.org
>
To change settings or unsubscribe visit:
>
birding-aus.org/mailman/listinfo/birding-aus_birding-aus.org
>
Birding-Aus mailing list
Birding-Aus@birding-aus.org
To change settings or unsubscribe visit:
birding-aus.org/mailman/listinfo/birding-aus_birding-aus.org
