Bottlenose Dolphin (Tursiops truncatus): Facts and Behavior

What does a bottlenose dolphin look like?

The bottlenose dolphin has a sturdy, streamlined body, a short, thick beak and a rounded forehead called the melon. Its name comes from that stubby beak, which reminded sailors of an old-fashioned bottle. The mouth line curves upward into a permanent “smile” that says nothing about the animal’s mood.

The color is usually gray: darker on the back, paler on the flanks and whitish or pinkish on the belly. This countershading helps hide the dolphin against dark water when seen from above and against bright surface light from below. The tall, backward-curving dorsal fin sits in the middle of the back. Nicks and notches along its edge are as individual as fingerprints, so researchers photograph fins to recognize the same dolphins year after year.

Each side of each jaw holds about 18–28 cone-shaped teeth, used for gripping rather than chewing. The dolphin breathes through a single blowhole on top of its head, which is its nostril. Its flippers still contain arm and finger bones, while the tail flukes and dorsal fin contain no bone at all.

How big is a bottlenose dolphin?

Adults measure 2–4 m (6.6–13 ft) and weigh 150–650 kg (330–1,430 lb). In most parts of the world they are 2.5–3.5 m (8.2–11.5 ft) long and weigh 200–500 kg (440–1,100 lb). Males are generally bigger than females: in Sarasota Bay, Florida, adult males average about 260 kg (573 lb) and females about 190 kg (419 lb).

Size follows water temperature. Dolphins living in cold water, such as those off eastern Scotland, tend to be large and bulky, which helps them hold on to body heat, while those in warm, shallow lagoons are usually smaller.

Coastal and offshore bottlenose dolphins

Scientists recognize two broad forms, or ecotypes. Coastal dolphins live in bays, estuaries, harbors and shallow inshore waters, often in resident communities that stay in the same area for generations. They are usually smaller and paler, with relatively larger flippers that help them turn quickly and shed heat. Offshore dolphins roam deeper water over the continental shelf and the open sea. They are larger and darker, their blood is better suited to deep diving, and some travel thousands of kilometers in a season.

The two forms can differ genetically, and the classification of bottlenose dolphins is still being worked out. In 2022, researchers proposed that the coastal dolphins of the eastern United States are a separate species, Tamanend’s bottlenose dolphin (Tursiops erebennus), and the Society for Marine Mammalogy accepted it in 2023. The IUCN still treats the common bottlenose dolphin in the broader sense. A related species, the smaller Indo-Pacific bottlenose dolphin (Tursiops aduncus), lives in warm coastal waters from East Africa to Australia.

Where do bottlenose dolphins live?

Common bottlenose dolphins live in tropical, subtropical and temperate seas around the world and are absent only from polar waters. They use an unusually wide range of habitats, from harbors, lagoons and river mouths to waters far out at sea.

In Europe, they occur from Scotland and Ireland south to the Mediterranean, with a distinct subspecies in the Black Sea. Well-known resident groups live in the Moray Firth in Scotland, Cardigan Bay in Wales and the Shannon Estuary in Ireland, and dolphins are regularly seen off Cornwall. In North America, they range along the Atlantic coast from Massachusetts to Florida, throughout the Gulf of Mexico and the Caribbean, and along the Pacific coast off California, Oregon and Washington, as well as around Hawaii.

What do bottlenose dolphins eat?

Bottlenose dolphins are carnivores that eat mainly fish, plus squid, shrimp, crabs and eels. The menu depends on where they live. Along the US Atlantic coast, croakers, spot and silver perch are typical prey, while dolphins in southern Spain’s Gulf of Cádiz take many conger eels and hake. They do not chew, but swallow prey whole, usually head first so that fish spines do not catch in the throat.

To find food they use echolocation, sending out rapid clicks and reading the echoes, and they also simply listen: many prey fish grunt, grind their teeth or splash. Hunting methods vary from place to place and are passed on by learning. Groups herd fish against sandbars or seawalls; in South Carolina and Georgia, dolphins drive fish onto muddy banks and briefly beach themselves to grab them; and Sarasota Bay dolphins use their tails to whack fish out of the water, sometimes 6 m (20 ft) into the air.

Social life, communication and intelligence

Bottlenose dolphins live in fission-fusion societies, in which group membership changes often, sometimes hour by hour. Coastal groups usually number from 2 to about 15 animals, while offshore dolphins may gather in hundreds. Mothers and calves form the closest bonds, and adult males often pair up with one or two partners in alliances that can last for many years.

They communicate with whistles, buzzing burst-pulsed sounds, touch and body language such as jaw claps and tail slaps. Each dolphin develops a signature whistle in its first year that others copy to call it, much like a name; read more in How do dolphins communicate? They can remember the whistles of former companions after more than 20 years apart.

Their brain weighs about 1.5–1.7 kg (3.3–3.7 lb), slightly more than a human brain. In 2001, two bottlenose dolphins at the New York Aquarium passed a version of the mirror self-recognition test. See How smart are dolphins? for what the research shows. Dolphins also sleep in an unusual way, resting one half of the brain at a time so they can keep surfacing to breathe.

Reproduction and lifespan

Females are pregnant for about 12 months and give birth to a single calf, usually tail first. Births can happen in any season but peak in warmer months. The calf nurses for about 20 months and stays with its mother for 3–6 years, learning where to find food and how to catch it. Females begin breeding at 5–15 years old, depending on the population, and then calve every 3–6 years; females as old as 45 have given birth.

Bottlenose dolphins can live 40–60 years in the wild, and females typically outlive males. The oldest known wild dolphin, a Sarasota Bay female named Nicklo, lived to 67. Find out more in How long do dolphins live?

Long-term studies in Sarasota Bay and the Moray Firth

Much of what we know comes from a few long-running field studies. The Sarasota Dolphin Research Program in Florida began in October 1970 and is the world’s longest-running study of a wild dolphin population. Run by Brookfield Zoo Chicago since 1989 and based at Mote Marine Laboratory, it has followed a resident community through six generations. Its work first described long-term male pair bonds, helped show that signature whistles act as names and measured how boats, fishing gear and pollution affect dolphins.

In Scotland, the Moray Firth holds the only known resident population of bottlenose dolphins in the North Sea, roughly 200 animals that range along the east coast. Researchers from the University of Aberdeen have photographed and followed individuals there for more than three decades, and the inner firth is protected as a Special Area of Conservation. These dolphins have also been seen attacking and killing harbor porpoises, a behavior compared in dolphin vs porpoise.

Predators, threats and conservation status

Large sharks, including bull, tiger, dusky and great white sharks, are the main natural predators, especially of calves. About 36% of Sarasota Bay dolphins carry at least one shark bite. Orcas occasionally prey on bottlenose dolphins in some regions.

Human threats are more serious. Dolphins drown as bycatch in gillnets, trawls and traps, swallow or become tangled in fishing line, and are hit by boats; about 1 in 20 Sarasota dolphins carries a scar from a boat strike. Feeding by people teaches dolphins to beg near boats and anglers, which raises these risks. Pollutants such as PCBs build up in their blubber, harmful algal blooms such as Florida’s red tides have caused mass deaths, and dolphins exposed to the 2010 Deepwater Horizon oil spill suffered lung disease and failed pregnancies. Dolphins are still taken in drive hunts in Taiji, Japan.

The IUCN lists the species as Least Concern (2019), although some regional populations are small or declining. In the US, all bottlenose dolphins are protected under the Marine Mammal Protection Act of 1972. In Europe, they are strictly protected under the EU Habitats Directive, with protected areas such as the Moray Firth, Cardigan Bay and the Lower River Shannon.

Bottlenose dolphins and people

The film and television series Flipper in the 1960s made the bottlenose dolphin famous, and it is the dolphin most often kept in aquariums. The US Navy Marine Mammal Program, based in San Diego, trains bottlenose dolphins to find sea mines. In Laguna, southern Brazil, wild dolphins and local fishers have cooperated for more than 150 years: the dolphins drive mullet toward the shore and signal with a distinctive movement when to cast the nets.

The friendly image is only part of the story. Wild dolphins can be rough with each other and with people, and a few solitary dolphins that became used to swimmers have injured them. The safest and kindest way to enjoy them is from a distance, from shore or from boats that follow local wildlife-watching codes.