Another Life: What do birds dream about?
A study of zebra finches found them practising their songs. Other birds need to stay more alert, so only one side of their brain goes to sleep at a time
After sunset: what avian dreams may come? Illustration: Michael Viney
This is the month of sunsets like bonfires, blazing up over the islands in luridly gilded flames or sinking redly and smokily into a frieze of purple storm clouds. As the last bar of crimson neon fades from the channel through the strand, a final chink-chink from a shadowy blackbird brings the day’s proceedings to a close. City blackbirds have been found to wake half an hour ahead of those in the country, and to stay active six minutes longer (all this in Munich, for a start), but here on an ocean hillside they enjoy sunset to the final glimmer.
The blackbird sleeps deep in a bush, its claws safely locked upon a twig – sleeps . . . perchance to dream?
Birds share not only sleep with mammals but spells of REM sleep, too – dreams betrayed by rapid eye movement and distinctive excitations of the brain.
What might a bird dream about?
A study of zebra finches found them practising their songs. The researchers recorded the pattern of neurons firing in the brain’s musical area as the birds sang in daytime, then played the song back to them as they slept. Their brains responded with identical patterns, while still sleeping and making no sound.
The zebra finches were Australian but were studied by neurobiologists from Chicago University, long a centre for the study of sleep and its deprivation. Once, long ago, I visited the laboratory of Dr William Dement, who now, at Stanford University, is a leading authority on sleep. He was studying the loss of REM sleep in cats, and I remember his subjects regarding me, somewhat woozily, from beneath the Frankenstein electrodes implanted in their skulls. Today such implants are internal, microscopic and able to monitor the electrical activity of individual brain cells.
A study of European blackbirds, in Poland this time, showed that much of their EEG pattern echoed that of mammals, while showing the behaviour common to most birds: opening one eye as they sleep,
In the state called unihemispheric sleep, one half of the bird’s brain is awake and alert while the opposite eye is taking a peek for predators. In the sleeping Polish blackbirds, the typical peek lasted from two to four seconds and accounted for perhaps 200 seconds in a night. This left plenty of time for REM sleep, but whether blackbirds singing in the dead of night are actually voicing their dreams aloud has not, it seems, been discovered.
Birds that sleep on the ground need to be especially watchful. Ducks and swans may have their heads turned backwards, bill tucked into the warmer air beneath their feathers, but they can still lift an eyelid. A video study of mallard ducks roosting in a group found that the birds sleeping at the edge spent longer with one eye open, looking outwards for threats, than those in the safer middle.