On Mon, Sep 05, 2011 at 07:22:52AM -0500, Chris Corben wrote:
> A couple of points arise from this. Firstly, I have never seen any
> evidence of Frogmouths sleeping. As far as I can tell, they are
> always awake and alert. I have watched them under a great variety of
> circumstances both in the wild and in captivity, and I have never
> seen one which seemed asleep.
> I have seen plenty of other birds which appeared to be asleep and
> were clearly unaware of things going on around them. But I don't
> know what sleep means to a bird, and if there is a range of states
> which they can be in, or how different groups of birds vary in this
> respect.
It seems we are just getting answers to these sort of questions.
Unihemispheric slow wave sleep with half the brain asleep and one eye
closed is known from some bird species, and individuals on the exposed
periphery of roosting flocks have been observed to enter this state more,
presumably because they are at greater risk of predation.
This very recent paper titled "Ostriches Sleep like Platypus":
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0023203
found Ostriches enter a slow wave sleep state with both eyes open and
look alert but motionless. Ostriches also enter a both eyes-closed REM
sleep state similar to human.
So a motionless Frogmouth with eyes wide open might be asleep.
Its speculated species which spend days aloft such as swifts could enter
slow wave sleep on the wing. EEGs might be still too cumbersome for
swifts but they are definitely small enough to put on a Frigatebird so we
should know more soon.
Frogmouths are also known to allow their body temperature to drop and
enter shallow torpor for several hours during the night or early morning.
I haven't seen it reported for Frogmouths but other birds which enter
torpor may have eyes open or closed.
Andrew
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