Hello Chris,
Thanks again for your interesting and detailed response.
Now that you mention Jack, he gave a fascinating lecture on this subject to the
folks at O'Relillys Bird Week some years ago - I have but a vague recollection
of the detail - such is the joy of getting older!
I do have a good picture of a Tawny Frogmouth in staring mode - I should
annotate it appropriately.
Cheers
Graeme
On 19/11/2013, at 9:41 AM, Chris Corben wrote:
> Hi Graeme
>
> There's an interesting aspect to this. The man to talk to is Jack Pettigrew,
> who has done a massive amount of work on the eyes of these creatures. I know
> he looked at Owlet Nightjars, but am not sure what he found.
>
> But because of my long involvement with Frogmouths, I do remember the story
> with them. They are apparently at least unusual in being able to swivel the
> eyes within their sockets. I thought Jack said this was very unusual in
> birds, but am not sure. But the case with Frogmouths is quite fascinating.
>
> Because they can swivel their eyes, they have two different modes of vision.
> In one mode, the eyes look out to the sides and then there is very little
> overlap, so their sight covers a very wide angle but without the bifocal
> overlap which gives a sense of depth. Like the vision you would expect of a
> Snipe! So this is well suited to looking for threats, but not for catching
> prey. In the second mode, the eyes swivel around to face the front, giving
> them a much narrower field of view but with broad bifocal overlap and good
> sense of depth. More like a Human or an Owl.
>
> If you watch a roosting Frogmouth in the daytime, you can see these modes
> very easily. Typically, a roosting Frogmouth perches in a very relaxed
> position, sort of like a Kookaburra in general pose. I am convinced they
> never sleep - certainly I have seen no evidence of it. They are constantly
> alert. If they see what might be a threat, they then strike the classic
> "broken branch" pose, where they stretch out their body and slim it down so
> it looks smaller and less conspicuous. In this pose, they watch you through
> one eye, looking out sideways at you and reducing the eye to just a slit,
> which isn't very conspicuous, and I think is the reason people think they are
> asleep - because the eye looks shut.
>
> If you then walk around them, they follow you with very inconspicuous head
> motions - keeping you in view with one eye. But typically there will come a
> point where they suddenly turn to face you, swivel their eyes around and
> stare straight at you with both eyes, at which time they take on a look which
> is much more owl-like!
>
> I don't know if an Owlet Nightjar can swivel its eyes.
>
> Cheers, Chris.
>
>
> On 11/18/2013 03:29 PM, Graeme Chapman wrote:
>>
>>> Hello Chris,
>>>
>>> Thanks for your interesting insight.
>>>
>>> Ref the eye-shine thing I'm attaching a close-up which shows the angle of
>>> an Owlet-Nightjars eyes ( pic 317201 on my website) - they appear to me to
>>> point largely to the side and also appear to very convex - quite odd
>>> looking really and it looks as though their peripheral vision might even
>>> allow them to look a long way behind them. Using a spotlight I suspect it
>>> wouldn't be easy to see both eyes at once. What do you reckon?
>>>
>>> Cheers
>>>
>>> Graeme
>>>
>>>
>>
>
>
> --
>
> Chris Corben.
>
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