Dolphins: Facts about the intelligent marine mammals that use tools to hunt

Dolphins eat many types of food, including fish, squid, octopuses, turtles, shrimp and crabs. Larger species, such as orcas, hunt and kill marine mammals, like seals, sea lions and other dolphin species. They can even hunt great white sharks and blue whales, the biggest creatures on Earth. Most dolphins eat between 2% and 10% of their body weight every day.

As part of the "toothed whale" group of animals, all dolphins have teeth, though some species have a lot more than others. Spinner dolphins have up to 240 teeth, while Risso's dolphins have only 14.

Dolphins send out high-pitched sounds and listen for their echoes to build an image of their surroundings. This technique is known as echolocation. They often hunt in groups, working as a team to trap fish or other prey. One clever hunting technique dolphins use is called bait balling, in which a group of dolphins herds a school of fish into a tight ball, making it easier to grab a quick meal. Groups of dolphins also force fish into shallow water and then gobble them up. This hunting method is called corralling.

Dolphins sleep, but they do it in a very different way than humans do. These creatures sleep with only half of their brain at a time, while the other half stays awake. This allows them to keep one eye open, which can watch for predators while half of their brain rests. Dolphins switch which half of their brain is asleep every few hours.

During this half-sleep, dolphins may rest near the surface, float motionlessly, or swim slowly. The awake half of their brain also controls their breathing. This is important because dolphins do not have gills like fish do. Instead, they must go to the water's surface to breathe. Unlike humans, who breathe automatically, dolphins must manually breathe, meaning that if they went totally unconscious during sleep like we do, they would suffocate or drown.

Additionally, this strange type of sleep also lets the dolphins keep moving their muscles, which helps them stay warm in cold water.

Newborn dolphins and their mothers don't sleep for the first few weeks after birth. Instead, the mother keeps swimming so the calf can stay safe and continue breathing.

Like humans, dogs, monkeys and other furry land animals, dolphins are mammals. This means they are warm-blooded and stay cozy in the ocean water thanks to a layer of fat called blubber. Along with other marine mammals — like whales, seals, sea lions and porpoises — dolphins must go to the surface to breathe air through blowholes on the tops of their bodies. They hold their breath while swimming and hunting underwater. Whereas some whale species can stay underwater for several hours, dolphins can hold their breath for only 10 to 20 minutes before needing to come back up for air.

Like most other mammals, dolphins give birth to live young. Dolphins usually give birth to only one calf at a time. Dolphin pregnancies last between 10 and 18 months, depending on the species. The calf is pushed to the surface immediately after birth so it can take its first breath.

The mother then feeds the calf with her milk for two to three years. This milk is incredibly rich and fatty, which helps the calf grow quickly. Calves then slowly learn from their mothers how to catch fish. Young dolphins stay with their mothers until they are around 5 to 10 years old, depending on the species. However, some orcas stay with their mother's pod for their entire lives.

Most dolphins are not interested in attacking humans, but they may act aggressively toward people in certain situations. Although dolphins are not usually dangerous to people, that doesn't mean humans should approach dolphins. They are usually friendly, but wild dolphins are still powerful predators and may become aggressive if they feel threatened. Males, in particular, can be territorial and may show aggression toward other dolphins or even humans.

In 2023, a woman swimming in a river in Bolivia needed 32 stitches after pink river dolphins attacked her, and several people were injured in a series of dolphin attacks off the coast of Japan. Even when they don't mean to be aggressive, dolphins can sometimes play rough, occasionally ramming or biting nearby humans.

Dolphins that are kept in captivity may become increasingly aggressive due to stress, confinement or poor treatment. Several people, including children, have been injured by dolphins while swimming with them in captivity. Captive dolphins have also repeatedly attacked their trainers. In 2022, for instance, a 23-year-old dolphin tried to drown its trainer during a live performance at Miami Seaquarium in 2022.

Orcas can also become aggressive in captivity. In a famous case in 2010, an orca at SeaWorld named Tilikum killed his trainer. However, orcas almost never attack humans in the wild.