Facts About Dolphins
Published October 8, 2026 · FactsSeeker
Dolphins are marine mammals with complex senses, varied diets, and social lives that differ among species. The facts below focus on what the San Diego Zoo Animals & Plants source supports, including classification, anatomy, sleep, sound, feeding, reproduction, size, and conservation.
Dolphins are cetaceans in a large dolphin family
Dolphins belong to the scientific order Cetacea, the same order that includes whales and porpoises. Within that order, the dolphin family Delphinidae includes 36 species, so dolphin is a family-level grouping rather than a single kind of animal. [1]
Some dolphin names include the word whale
Common names can make dolphin classification confusing because some members of the dolphin family are called whales. The source specifically identifies the killer whale as the largest dolphin, even though its common name does not use the word dolphin. [1]
Dolphin appearance varies widely by species
Dolphins are not all the same color; the source describes colors ranging from white, pearl, and pink to darker brown, gray, blue, and black. It also describes smooth skin, flippers, a dorsal fin, a streamlined body, and a long, slender snout with about 100 teeth. [1]
Dolphins breathe through a blowhole at the surface
A dolphin’s breathing opening is a single blowhole on top of the head. The blowhole has a flap that opens to reveal a pair of nostrils, and dolphins use it when they come to the surface to breathe. [1]
Sleeping dolphins remain close to the surface
The source explains that sleeping dolphins do not sink. Instead, they float about 10 inches (25 centimeters) below the surface, and small fluke movements periodically bring them up so they can breathe through the blowhole. [1]
Each eye can move independently
Dolphins have an eye on each side of the head, and each eye can move independently. This arrangement lets them see ahead, to the side, and behind them, and the source says they see well both underwater and above water. [1]
River-dwelling dolphins may rely less on vision
The source says dolphins that live in rivers have much less developed vision than other dolphins. It frames the reason as probable rather than certain: murky river water may make strong eyesight less useful. [1]
Dolphins use clicks, whistles, and many other sounds
Dolphins use clicking sounds for echolocation, and many use whistles to communicate with their pod. Researchers have also described dolphin sounds as screams, calls, moans, trills, grunts, squeaks, and even a creaky-door-like sound. [1]
Some bottlenose dolphin sounds may signal mood
The source is careful to say that bottlenose dolphin researchers think certain sounds reflect emotional states. Slow clicks and high-pitched whistles are interpreted as signs of contentment, while harsh, low squawks are interpreted as annoyance. [1]
Dolphins receive sound through the head and jaw
Dolphin ear holes are tiny, but the source says they probably have exceptional hearing. It explains that dolphins receive sounds through the jawbone and head, with vibrations passing into the small bones of the inner ear. [1]
Echolocation helps dolphins navigate and hunt
All dolphins make sounds that travel underwater, bounce off objects, and return as echoes. This echolocation helps them find food or avoid predators, including in dark or murky water, and river dolphins use it for fishing in muddy water. [1]
Dolphins live in many ocean settings and eat varied prey
Dolphins are found in all the oceans of the world. Some live mainly along coastlines while others live far out at sea, and most dolphins eat fish, octopus, squid, and shrimp; killer whales have a broader diet that includes seals, smaller whales, penguins, birds, and small walrus. [1]
Some dolphins cooperate while feeding
The source describes dolphins working together to eat, including herding schools of fish for group feeding. Some use clicking sounds while herding fish, and bottlenose dolphins may rush onto mud banks to catch stranded fish. [1]
Dolphin schools can be highly social
Dolphins live and play in schools that may range from five to hundreds of animals. The source also describes coordinated swimming and says dolphins may work together when another dolphin is sick, hurt, or giving birth by helping push it to the surface to breathe. [1]
Life span and reproduction differ by species
The source gives dolphin life span as 20 to 90 years, depending on species. It also says gestation is usually 10 to 12 months for most species, with 1 young at birth, and birth weight ranging from 10 to 400 pounds (4.5 to 180 kilograms), depending on species. [1]
Dolphin size ranges from small dolphins to killer whales
The source lists the killer whale as the longest and heaviest dolphin, at 23 feet (7 meters) and up to 4.5 tons (4.55 tonnes). At the smaller end, it lists Heaviside's dolphin at 3.5 feet (1.2 meters) and 88 pounds (40 kilograms). [1]
Several human pressures affect dolphin conservation
The source says hunting, pollution, and human development along coastlines and rivers have seriously affected some dolphin populations. It also identifies dams, habitat loss, and fishing nets as problems, notes an international dolphin-conservation agreement from 2000, identifies Hector's dolphin as endangered, and says bottlenose dolphins are protected in US waters by the Marine Mammal Protection Act of 1972. [1]
Sources & further reading
These facts summarize a San Diego Zoo Animals & Plants page. Dolphin details vary by species, and several statements are framed by the source as depending on species, probable explanations, or researchers’ interpretations.
Sources checked 2026-10-08. Our approach to facts · Suggest a correction