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.
===============================
To unsubscribe from this mailing list,
send the message:
unsubscribe
(in the body of the message, with no Subject line)
to:
http://birding-aus.org
===============================
|
