birds' sleep requirements

To: "birding aus" <>
Subject: birds' sleep requirements
From: "Judie Peet" <>
Date: Fri, 9 Mar 2001 13:02:32 +1100
 Dear birding-ausers,
I thought you might be interested in seeing the little article that resulted from my bird sleep question. This was written for the Dubbo Field Nats' monthly journal, Field Notes. Once again, many thanks to all who helped with info or anecdote, and thanks to Russell to for providing a place where such questions and answers can flash to and fro with astonishing ease. I am working to a deadline, and can't think of any other way I could have gained so much help.
Judie Peet
Willie Wagtail Won’t Stop Whistling!
A question: Why do Willie Wagtails call and twitter at night, especially hot moonlit summer nights? Don’t they ever sleep?
David Sloane
David this is a difficult question. Very little is known about bird sleep, although some recent studies have shown that birds are able to sleep with one eye open and one side of their brain awake. Amazing huh?  Called unihemispheric slow-wave sleep (USWS), this ability is thought to have developed because birds need to be partly wakeful as protection from predators. (Dolphins and whales have this ability to some extent too, being able to rise to the surface to breathe whilst sleeping underwater.)
It’s not only Willie Wagtails that “call all night” – although an unfortunate would-be sleeper in Adelaide has recorded a Willie Wagtail calling every 15 seconds through the night!  We once listened to Grey Fantails calling all through the night when camped at Weddin Mountains, and Koels are renowned for night-time calling too.   Night calling has not been observed closely enough for anyone to say with certainty that it was the same bird calling continuously though!  Maybe the bird’s partner takes over, or perhaps another male joins in to provide that continuous sound.
The night calling usually occurs during breeding season, and has the dual purpose of (hopefully) enticing a mate, and setting up all-important territorial boundaries. While it is thought that birds are able to have short ‘catch-up’ naps when needed, studies involving the English Blackbird show that night calling places great stress on the male bird, increasing the chances that it will lose strength and dominance, and be replaced by another male. What a dilemma!
The ability to “half sleep” is believed to allow migrating seabirds to fly for extended periods on “auto pilot”, although this has not yet been proven scientifically.
It’s an interesting topic for speculation , leading us to consider our own almost unused ability to control sleep. Most of us will have at some time, gone to bed saying to ourselves, “I MUST wake up at 4 o’clock”.  Although this may be some hours earlier than we usually wake, we find ourselves awake and waiting  for the alarm at 5 to 4 the next morning.  If we need to wake for a sick child or relative, we will do so at the slightest noise – a noise well below that needed to wake us normally.
Thank you for posing such a fascinating question David, and thanks to the people on the  birding-aus list who generously helped with information. Special thanks to Dr Jim Davis, editor of Interpretive Birding Bulletin. For more information about IB Bulletin see
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