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Songbirds rehearse songs in sleep
Singing and dreaming
Much of what is known about how a bird's brain works comes from songbirds. The same brain regions are stimulated when a songbird sings and when it sleeps, which suggests birds dream.
Reconsidering information
Birds can also reconsider information instead of simply reacting. Incoming information does not have to go straight down to the muscles. It can be sent back to the forebrain, looped between the forebrain and the thalamus, and reshaped before the bird acts. A person does the same thing when the urge to walk out of a talk gets reconsidered into staying a little longer.
Two halves of the brain
The two halves of a bird's brain are less connected than a person's. Because of that, a bird can sleep one half of its brain while the other half keeps considering the world.
How do researchers know birds dream?
In a 2000 study in the journal Science, Amish Dave and Daniel Margoliash recorded from neurons in the brains of sleeping zebra finches. The neurons fired in patterns that matched the ones seen when the birds sang, as if the song were being replayed. The patterns were most similar to the birds' own song, not to other songs. Scientists take this as evidence that the birds were rehearsing the song in their sleep.
How can half a bird's brain sleep?
Many birds can show unihemispheric slow-wave sleep, in which one half of the brain shows the electrical pattern of deep sleep while the other stays awake. Niels Rattenborg and colleagues found in 1999 that mallard ducks at the edge of a group kept the eye facing outward open, and that the opposite brain hemisphere stayed awake. This lets the bird watch for predators while resting. Dolphins and some seals also sleep with one hemisphere at a time.
Why would sleep help a bird learn its song?
Young songbirds learn their songs by listening to an adult tutor and then practicing. In a 2005 study, Sylvain Derégnaucourt and colleagues found that young zebra finches sang worse after a night of sleep, then improved over the following day. The researchers proposed that sleep reorganizes the song memory for later practice. A bird that is disturbed during sleep learns its song less accurately.