Why are dolphins easy to train?

If you have visited a marine park, you probably know which animals steal the show: the dolphin(s). They delight visitors with their stunts. They ring bells, blow horns, and they even play basketball. Using their powerful tail fins, they "walk" backward in the water.

Social, playful, and curious, dolphins get along with humans well. They learn to do tricks quickly. Sometimes they make up their own. To teach a dolphin some tricks, a trainer uses its natural abilities. For example, dolphins often jump out of the water. So it's a short step to teaching the dolphin to jump through the hoops or over bars. underwater, dolphins use a sonar system of rapid clicks to navigate. With this system, a dolphin can pinpoint an object tossed into the water by a trainer. The animal can retrieve the object within seconds.

Dolphins, also called porpoises, are toothed whales. They are not fish, but they are mammals--animals that, as babies, drink milk from their mothers. Mammals include such intelligent animals as monkeys and apes. Yet some scientists think that dolphins, with their large and well- developed brains, may possess more intelligence than do monkeys and apes.

To communicate with one another, the dolphins whistle, squeak, growl or even moan. Some scientists think that these animals eventually can be trained to communicate with humans through a language of signs and symbols.

How can birds know when to migrate?

Flying on a straight course, "Sandhill" cranes head north to their summer home. Each spring, the cranes fly from Mexico and the southern part of the United States to Canada and Alaska. In the fall, they again head south. Large numbers of birds make similar round- trips every year. They migrate mainly to find food, better weather conditions, and places to breed and to raise their young/babies.

Perhaps you, like some scientists, have wondered how migrating birds know just when to come and go. Scientists believe that changes in the hours of daylight are the most important signal. As days grow longer in the spring, the increased periods of the sunlight cause changes in the birds' bodies. The birds eat more to store fat for fuel. They grow restless. Soon they take off for their summer homes. the same thing happens in the fall, when days start getting shorter. Changes in the weather and a shrinking food supply may also help the birds know when it's time to move on.

Besides knowing when to migrate, birds seem to know exactly where they're going. Most follow the same routes every year. To find their way, they use their keen senses to respond to a variety of clues. These include landmarks, such as rivers and mountains, and the position of the sun and the stars. scientists continue to study other factors, as well, that may help the birds navigate on their long journeys.

Do cats and dogs dream?

If three little kittens did lose their mittens, they might have dreamed about it the same night. Cats and dogs do dream. In their dreams, they probably relive exciting or frightening events of the day.

When scientists studied the sleep of cats in a laboratory, they found that the cats first went to a quiet state of sleep. The cats' eyes moved slowly under its lids. Then, after a few minutes, they eyes moved rapidly and jerkily. Brain- wave recordings showed that the animals had entered a sleep state called REM--for rapid eye movement. Throughout their sleep, the animals passed back and forth between the deeper quiet state and REM sleep.

Humans experience the same sleep states. Studies have shown that humans dream only during the REM sleep, so scientists think that cats and dogs dream then as well. Scientists believe that cats and dogs dream then as well. Scientists believe that REM sleep serves as a useful purpose for cats and dogs. In this state, the animals sleep lightly. They wake from time to time and inspect their surroundings for danger.

A dog that is dreaming may whine, pant, bark and wag its tail. Sometimes, it makes running movements. A cat usually lies more quietly, but it may twitch, or swat with its paw.

If your sleeping pet appears restless, don't worry. It's probably just living in a dream world.