Entering the World of Dolphins:

Research So Compelling That Andy Read Rarely Takes a Holiday p.2

So how different are they?

Consider the simple act of drinking, something bottlenosed dolphins, never do since they live in salt water which is "effectively a desert," Read said. "There is no fresh water available to them in their entire lives. So they need to obtain fresh water from their food through metabolic digestion." That means if dolphins becomes sick and stop feeding, dehydration becomes as much of a concern as starvation.

Because of their salty environments dolphins have especially efficient kidneys for processing wastes. In addition, their lungs are more efficient air handlers than are human lungs. Lungpower aside, dolphins "are able to store more oxygen in their bodies than we are," he said.

The way dolphins breathe is different. While people do it automatically, dolphins are "voluntary breathers," Read said. That means "when they lose consciousness, they won't breathe. That's why we think dolphins probably never experience sleep like we do." In fact, research by a Russian physiologist suggests they "rest kind of one hemisphere of their brain at a time. They may go into a state of quiescence, but they don't sleep very deeply."

Even though dolphins have "an inner ear system very much like ours," evolution long ago "streamlined" away dolphin's external earlobes, Read said. Nature substituted fat pads in their lower jaws to transmit sounds to their inner ears. While their lungs breathe air in and out, they don't use those to power sound emissions either. Instead of exhaling air over vocal chords, scientists are discovering that dolphins use what are called "monkey lips" to make sound instead of exhaling air over vocal cords.

"That's what they look like in medical imaging," he explains. Those "lips" work by vibrating when recyclable air from sacs in the animals' heads pass over them. Findings as new as those presented at the last Society of Marine Mammalogy meeting are showing that there isn't just one dolphin sound system but two. One produces the kind of high frequency sounds that attenuates very quickly in water, while the other system creates lower frequency sound "that can travel longer," he said. "If you have both systems, you're capable of doing different things with your sonar. It's a very recent discovery. We have no idea how they do that."

What's clearer is that dolphins' sonar-like sound emissions can be used for "echolocation" in water in a manner similar to the way bats use ultrasonic pulses to navigate in the dark. But dolphin sound waves are emitted not though their mouths but rather through fat deposits in their large foreheads, creating a focused beam analogous to a flashlight. In essence, a dolphin's forehead serves as "an acoustic lens," according to Read. "I don't think it's possible for humans to imagine what it's like to have a sensory system like this. In the same way we can use ultrasound to look at a human fetus, a bottlenose dolphin can see inside a pregnant female dolphin to find out the size and gender of its fetus. They also can look inside each other to see if they have a full stomach, the size of their testes or condition of their ovaries, whether a female is ready to ovulate." These same special talents make dolphins great mine detectors.

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