You may have heard that dolphins sleep with only half of
their brains at a time. Like me, you may have assumed that, while the awake
hemisphere was capable of preventing the animals from drowning, it wasn’t completely alert. Not so. Apparently, dolphins can respond to echolocation and training
cues with full concentration indefinitely. Or at least, for the fifteen straight days demonstrated by this study.
Researchers from marine mammal programs in San Diego, led
by Brian Branstetter of the National Marine Mammal Foundation, asked two
dolphins (SAY and NAY) to search their water enclosure for simulated
echolocation targets. Upon detecting a target, the dolphins could press a
response paddle and receive a reward. After training, the dolphins each
participated in two 5-day sessions of round-the-clock target simulation. Both
of the dolphins maintained a correct response rate of over 75%, but because SAY
did a little better (she was correct 95% of the time), she got the honor of
participating in a 15-day test. That test was actually supposed to last thirty
days, but was cut short by a storm. SAY’s performance remained strong
throughout this longer interval.
SAY
Credit: Brian Branstetter
During unihemispheric sleep when only half their brains
are awake, dolphins are not merely maintaining breathing and other bodily
functions. They can respond to their surroundings with full alertness. If you
consider that many dolphin populations are at constant risk of attack from
sharks, perpetual vigilance sounds like a great idea.
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