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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 www.ibirding.com
Judie
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