Dolphins are very intelligent animals, and researchers have designed experiments to find out what that means. In the mark test, researchers put a mark on a dolphin where it could not see it, then watched whether the dolphin used a mirror to look at the mark. In a 2001 study, two bottlenose dolphins used a mirror to examine marks on their bodies, and at that time only humans and great apes had shown convincing mirror self-recognition.

Two dolphins in Louis Herman's lab learned a vocabulary of about 50 words, which they used to build more than 1,000 different commands of up to five words. Whistles tell researchers about a different side of dolphin communication: each bottlenose dolphin develops its own signature whistle, and scientists think a signature whistle works like a name. Signature whistles make up about half of a bottlenose dolphin's whistles, and wild bottlenose dolphins often copy each other's signature whistles. In 2006 researchers played synthetic whistles to Sarasota Bay dolphins, and in 9 of 14 cases a dolphin turned toward the speaker more often when the whistle resembled a close relative's.

Dolphins find things by making sounds that bounce off objects and return as echoes. A waxy, lens-shaped part in the forehead, called the melon, focuses the clicks into a beam, and the echoes are picked up through the lower jaw. Low-frequency clicks travel farther but give less detail, so a dolphin raises the frequency of its clicks as it moves closer to an object. Dolphins are good at detecting air spaces, so they can find fish with air-filled swim bladders by echolocation. Some dolphins also find fish by listening for the sounds the fish make, and the U.S. Navy trains bottlenose dolphins to find and mark mines on the sea floor.

Bottlenose dolphins sleep with one half of the brain at a time, which is called unihemispheric slow wave sleep. When a dolphin sleeps, half of its brain stays awake. Near shore, a bottlenose dolphin comes up to breathe about two times a minute. A dolphin's brain has no sense of smell. Its belly can turn pink when it is active, which helps it release extra body heat.

At Laguna in southern Brazil, wild bottlenose dolphins chase mullet toward fishers standing in shallow water, and 86 percent of the mullet that fishers caught there came from catches synchronized with dolphins. Calves learn how to hunt mostly by watching their mothers. In Shark Bay, Australia, some dolphins wear sea sponges on their snouts while they search the sea floor for food, and calves can learn to use sponge tools from their mothers. Some bottlenose dolphins also strand-feed, rushing onto mud banks or the shore to catch fish stranded there.

Several bottlenose dolphin die-offs have been linked to harmful algal blooms such as red tide. As of November 2026, getting tangled in fishing gear is one of the main threats to bottlenose dolphins. Researchers have studied the dolphins of Sarasota Bay since October 1970. As of November 2026, in that bay a boat passes by a dolphin every 6 minutes, and 1 in 20 dolphins there has a scar from a boat collision. The IUCN Red List lists the common bottlenose dolphin as Least Concern, as of November 2026.

The baiji was a species of China's Yangtze River that used sonar, and as of November 2026 the record shows that in December 2006 an expedition on the Yangtze found no baiji, after which its leader said the species was functionally extinct. Overfishing and ship traffic, whose engines interfere with the sonar baiji use, were likely the main reasons for the baiji's decline.

In the United States, bottlenose dolphins are protected by the Marine Mammal Protection Act of 1972, and feeding wild dolphins is harmful because it teaches them to come close to boats and people. As of November 2026, people should stay at least 50 yards (46 meters) away from wild dolphins.

Words to know

• echolocation: finding by echoes
• synchronized: timed together
• functionally: in practice
• algal: of algae
• vocabulary: known words