Illustration by Garry MarshallSource: The Greenpeace Book of Dolphins
2. A round organ called the melon focuses the sound beam.
3. The sound strikes an object and returns toward the dolphin.
4. The panbone in the dolphin’s jaw receives the echo; fatty tissue behind it transmits the sound to the middle ear and from there to the brain.
5. Continuously transmitting and receiving clicks, the dolphin reacts to the time lapse and strength of the signal to judge distance and home in on an object.
In 2001, dolphins joined the ranks of chimpanzees, orangutans, and humans as the only species to pass the “mirror test,” considered a benchmark for self-awareness. When scientists marked a pair of dolphins on areas of their bodies not normally visible to them, the aquatic mammals raced to a mirror and twisted their bodies to expose the marks.
Because the bodies of these mammals must be streamlined to move quickly through water, male reproductive organs are inside the body. Body warmth can damage sperm, however. So warm-blooded dolphins have evolved an elaborate heat-exchange system of woven veins and arteries. Veins that carry cooled blood from the tail lower the temperature of interwoven arteries that bring the warmer blood to the testes.
In addition to using sight, dolphins can locate objects by echo. They emit and process as many as 700 clicking sounds per second to detect the size and location of objects hundreds of meters away. This capability is invaluable underwater, where visibility is limited.
Using echolocation, a dolphin can discriminate between objects that differ by as little as 10 percent in volume or surface area, even in noisy environments. See How It Works (below) for a step-by-step explanation of echolocation.
The U.S. Navy has used dolphins to tag deadly mines for detonation. On such missions, dolphins have found softball-size targets at a range of 200 yards or more.
Dolphins give birth to one offspring, called a calf, at a time. At birth a bottlenose dolphin calf is about 3 to 41/3 feet long, and will grow to approximately 13 feet.
Highly sociable, dolphins live in groups called pods. Dolphins from separate pods occasionally interact.
Dolphins can empty and refill their lungs in less than 0.2 seconds. As the dolphin breathes, the air leaves its blowhole at speeds of more than 100 mph.
Dolphins must be conscious to breathe. So they shut down only half of their brain at a time and take short naps, floating just below the surface and slowly rising to breathe.
–compiled by Bob Sillery