Dolphins are the most heavily researched of all whales with more than 300 in captivity in the United States alone. Most are on exhibition in aquariums, while others are in marine mammal research facilities at universities and private foundations.

      Numerous scientists have studied the physiology of dolphins to learn how they, as mammals, have adapted to diving, while others have tried to determine how intelligent they are. Some believe they are as intelligent as dogs and in some cases rival the intelligence of humans. The U.S. Navy has trained dolphins for locating and retrieving objects such as tools and equipment underwater.

      But dolphins' ability to communicate continues to intrigue researchers most. Dolphins have been trained to respond to hand gestures or even voice commands of up to three words such as "swim, hoop, jump."