I don't know anything about the mechanisms behind "sleep", but I have seen some
striking alternative strategies to the "sleep" strategy used by humans.
It is intuitive that whales and dolphins do not "sleep" the same way we do,
because they have to keep swimming their entire lives. Some rest at the water
surface occasionally, but most never do. Sperm whales show a behaviour pattern
none as "logging" in which they lie at the surface for half an hour or so,
breathing. Perhaps they are asleep. Baleen whales show a pattern also termed
"logging" where they move slowly and steadily in a straight line with fairly
constant timing in the breathing and diving sequence. It is not unusual to see
them suddenly "wake" from this pattern when confronted with an obstacle such as
a boat. I once saw a fin whale surfacing under a massive floating log once only
to wake suddenly and make some last minute and energetic manoeuvres to avoid
collision, and then go back to logging. They also
spontaneously "awake" and go into less automated and more diverse behaviour
patterns.
A Christmas Island Frigatebird that we satellite-tracked in 2006 flew about
5,000 km in 27 days without landing. Altimeter loggers on Great Frigatebirds
have shown that they spend more than 50% of the time "at sea" soaring in
thermals under cumulus clouds thousands of metres above sea and land. Their
wings would lock in place but they would still need to sense and steer to
remain in the thermal. Yet frigatebirds do appear to sleep on the nest, often
with the head and neck hanging vertically below the nest, eyes firmly shut, and
totally oblivious to noise such as ecologists counting nests, yelling to one
another, etc.
Frigatebirds and whales might use "unihemispherical sleep" but I doubt that it
would be the same thing in the two groups, since their evolutionary histories
are are so different. And how would a storm-petrel sleep in a 10-day gale in
the southern ocean? This would surely require staying fully awake for however
long was necessary.
Semantically, either only humans "sleep" like humans do, or "sleep" has many
forms and humans only experience one.
David James,
Sydney
==============================
From: Andrew Taylor <>
To: birding aus <>
Sent: Saturday, 10 September 2011 9:43 AM
Subject: sleep in Frogmouths & other birds
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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