Do dolphins sing like whales as they sleep? (1/30/12)
Many secrets arrive with the night.
Recently researchers at Universite de Rennes 1 in France decided to hook up microphones to listen to dolphins. No one seemed to know what sounds they made – especially in sleep.
The dolphins made a lot of noise.
However, 1% of their vocalizations sounded nothing like their vocalizations during the day. The researchers were astounded. They thought they were listening to whale music.
But there were no whales in the amusement park where the dolphins perform their shows. None of the dolphins had ever met or seen any whales.
Yet each day the amusement park played the songs of whales.
The researchers wondered if the dolphins might be “learning” the whale songs and then repeating them at night. The researchers were concerned if others would agree. So they then asked audience members to listen separately to the new dolphin sounds, and then to whale music. When asked to classify each, as discussed in a recent edition of “Science”, 76% of the humans classified the night-time dolphins “songs” as whale songs.
Are dolphins learning “whale” as they rest and sleep?
Dolphin Sleep – One Hemisphere at a Time
Dolphins differ from humans in many ways. One of the most prominent in their form of sleep – one hemisphere at a time. A dolphin can be in REM sleep, presumably dreaming along, in one hemisphere, and remain in a state of quiet wakefulness in the other half of its brain.
In other words, dolphins never have to “turn off” consciousness.
As they undergo their night-time version of sleep, dolphins often swim in circles. As they roll round and round they sometimes vocalize. Most of the “whale” sounds were picked up between midnight and 3 AM – prime time for dolphin sleep.
Dolphins and Whales
Are dolphins and whales very different?
Certainly to legislation. People who have watched the Oscar award winning documentary, “The Cove” which filmed the systematic bludgeoning of dolphins in a small Japanese inlet know that legal protection of dolphins is not like that of whales. Only some species of whales are hunted. However, whales and dolphins are both cetaceans – a word which means “whale.” Many a zoologist thinks of dolphins as “mini” whales, with somewhat different behavior and smaller size.
Paul Tyack, a dolphin researcher at St. Andrew’s University in Scotland, thinks the dolphin noises may not actually be repetitions of whale sounds. He notes that dolphins vocalize widely – and that he has heard them in the wild make similar forms of “song.”
Perhaps fellow cetaceans do make similar sounds. And these French dolphins are performers trained in recurrent mimicry.
Memory and Rehearsal
It’s intriguing that the dolphins might be repeating whale or other sounds while they sleep. It’s quite consistent with what’s known of memory consolidation in other mammals – like humans.
When memories are encoded within our daytime brains, they generally last briefly. Throughout the night in deep sleep and parts of REM, “playbacks” of memory occur. Much of the circuitry involves a kind of conversation between the cortex and the hippocampus, a major memory area.
It appears that new memories are “played in” to different areas of cortex, allowing them to be encoded as more permanent storage. Yet non-memory storage appears to be truly permanent. It may take many years for memories to stick so well that they cannot be “dislodged.” And as John Medina writes in his book “Brain Rules,” memories are remade every time they’re retrieved.
So the dolphins may be repeating whale songs in their sleep – as mammals repeat newly learned information throughout the night. Some of it may stick, be summarized, and appear in more permanent memory.
For dolphins only “sing like whales” at night. Their “whale” songs may be sung during the night and sleep, but never during the day.
Similar effects can occur in people. In sleep many memories are summarized, framed, placed into permanent memory – but often in ways not conscious to us.
Perhaps we too sing like whales in our sleep – if only in our minds. And no one hears us.
Or we simply don’t remember.
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