I Can’t Sleep - Dolphins | Can’t Sleep? Learn About Flipper

Episode Date: August 5, 2026

Dolphins have fascinated people for thousands of years with their intelligence, social behavior, and remarkable lives beneath the waves. This episode explores what dolphins are, where they live, how they communicate, and the adaptations that make them some of the ocean’s most successful mammals. Along the way, you’ll hear about echolocation, pods, playful behavior, and the many species of dolphins found around the world. It’s steady and consistent, with no whispering and no sudden changes, just enough to give your mind something to follow as you wind down. Happy sleeping! Read with permission from Dolphin, Wikipedia (https://en.wikipedia.org/wiki/Dolphin), licensed under CC BY-SA 4.0. — Ad-free episodes: ⁠icantsleep.supportingcast.fm⁠Have a topic in mind? ⁠Request a topic⁠ Learn more about your ad choices. Visit ⁠megaphone.fm/adchoices Learn more about your ad choices. Visit megaphone.fm/adchoices

Welcome to the I Can't Sleep podcast, where I help you drift off one fact at a time. I'm your host, Benjamin Boster, and today's episode is about dolphins. Dolphins belong to a surprisingly large family. 40 living species, to be exact, spread across five different taxonomic families. There are the oceanic dolphins, the family of most of his picture, and then four families of river dolphins, adapted to fresh water and brackish environments from the Amazon to the Ganges. One of those river families, the Baiji or Chinese river dolphin,

appears to have slipped into extinction sometime in the early 2000s. All of them fall under the larger category of toothed whales, which means they share evolutionary lineage with belugas, narwhals, porpoises, sperm whales, and beaked whales. The size range is staggering. At the small end there's Maui's dolphin, barely longer than a tall human, about five and a half feet, and weighing about 50 kilograms. At the other extreme sits the orca, the apex predator of the group, stretching past nine meters and tipping the scales at ten tons.

Sexual dimorphism shows up in many species, with males generally larger than females. What they all share is that torpedo shape. Streamlined bodies, four limbs evolved into flippers, no external hind limbs to speak of, just vestigial pelvic bones tucked inside. and a horizontal tail fluk that drives them forward they're faster and more agile than seals though not quite as flexible some dolphins hit brief bursts of twenty-nine kilometers per hour and they can leap nine meters into the air their conical teeth are built for grabbing fast-moving prey fish squid shrimp hearing is exceptionally well developed

adapted for both air and water, so refined that some blind dolphins manage to survive. Certain species dive to great depths. They all carry a thick layer of blubber under the skin to insulate against cold water. Dolphins live mostly in open ocean, though some thrive in rivers and coastal zones. Most prefer warm tropical waters, but a few species like the right whale dolphin favor colder climates. They are carnivores feeding largely on fish and squid, though the larger species, orcas especially, go after seals or other dolphins,

large fish like sharks and tuna, even seabirds on occasion. males mate with multiple females each year, but females only reproduce every two to three years. Cabs arrive in spring and summer, and mothers shoulder all the caregiving. In some species, mothers fast while nursing for an extended stretch. Social complexity defines dolphin life. They live in what researchers call fission-fusion societies,

Fluid groups or pods that constantly shift in size and membership. Communication happens through a variety of vocalizations. High-pitched clicks, whistles, burst pulse sounds. Echo location lets them navigate and hunt with precision. The name dolphin traces back to ancient Greek. Delphus, related to Delphus, meaning womb. The idea was something like a fish with a womb, an early recognition that these animals didn't quite fit the usual categories. The word traveled through Latin, delphinus, into medieval Latin as dolphins, then into Old French as a dolphin, which eventually gave English the spelling we use today.

In some older English dialects, they were called meerswine or sea pig. Usage of the term can be a little loose. Dolphin generally covers most species in the oceanic dolphin family and the river dolphin families. Meanwhile, the Mahimahi fish is sometimes called dolphin fish, which adds a layer of confusion. In everyday speech, people use whale for the larger cetaceans and dolphin for the smaller beaked ones. Though that's not a strict biological line. The bottlenose dolphin is so familiar that dolphin often means that species by default. Interestingly, six species commonly thought of as whales, orcas, melon-headed whales,

pygmy killer whales, false killer whales, and two species of pilot whales, are actually classified as dolphins. Porpoises, by contrast, belong to a different family entirely. They have shorter beaks, spade-shaped teeth, and different behavior patterns. A group of dolphins is a school or a pod. males are bulls, females are cows, young ones are calves. The dolphin lineage reaches back to land-dwelling mammals. Around 48 million years ago, their ancestors split off from a group that included the Indohias. An extinct chevrotin-like ungulate, think of a small deer-like creature.

The earliest cetaceans, the Archaeocetes, took to the water around 49 million years ago and became fully aquatic within 5 to 10 million years. The fossil record shows a gradual transformation. Ambulocetis, around 49 million years ago, developed a hearing system that channeled vibrations from the jaw to the inner ear. Protocetus, about 43 million years ago, showed a streamlined body and tail flukes. Basilosaurus, 35 million years back, had nasal openings migrating toward the top of the skull, and four limbs modified into flippers.

By 34 million years ago, hind limbs were shrinking and eventually disappeared in the first true toothed and baling whales. Modern dolphins still carry two small rod-shaped pelvic bones, remnant of that terrestrial past. Today, the closest living relatives of cetaceans are hippopotamuses. They share a semi-aquatic ancestor from about 60 million years ago. Around 40 million years ago, the lineage split. One branch became cetaceans, The other became anthracotheirs, which went extinct at the end of the Pleistocene, leaving only hippos behind. Dolphin anatomy is a study in adaptation. Torpedo-shaped bodies, non-flexible necks, limbs turned to flippers, a tail fin, and a bulbous head. The skull has small eye sockets, along some.

snout, and eyes set on the sides, no external ear flaps. Size varies widely from the tiny Maui's dolphin to the massive orca. Several species show female biased size differences, with females larger than males. Conical teeth, unlike the spade-shaped teeth of porpoises, are designed for catching swift prey. breathing involves expelling stale air through the blow-hole in an upward blast then inhaling fresh air the spouts are small and not especially distinctive blubber thickness varies with climate It provides buoyancy, some protection from predators, and energy reserves. But its main job is insulation. Cavs are born with a thin layer that thickens at different rates, depending on where they live. The skin is specialized for protection, fat storage, heat regulation, and sensory perception.

It's made of an outer epidermis and an inner layer of blubber, which includes the dermis and subcutus. Dolphin's skin has a smooth, almost rubbery texture. There's no hair and no glands, except for mammary glands. Newborns have a line of hairs on both sides of the rostrum, the jaw, about 16 to 17 centimeters in total length. The epidermis lacks keratin and features a complex interweaving of structures

that increase the surface area between skin layers. Thickness varies by species and age. Blubber sits within the dermis and subcutus. The boundary between dermis and fat layer is gradual. with collagen fibers running throughout. Thickness depends on health, development, location, reproductive state, and feeding success. It's thickest on the back and belly.

Unlike simple fat, blubber contains a fibrous network of connective tissue. It streamlines the body and forms specialized structures like the dorsal fin and tail flukes. Nerve endings resembling small onion-like configurations appear in the superficial dermis. Mechanoreceptors tucked into the interlocking ridges of skin layers. These nerve endings provide highly refined sensory perception, the body's ability to sense its own position and movement.

Dolphins are sensitive to vibration. and small pressure changes. Blood vessels and nerve endings run through the dermis. In the dorsal fin, flukes, and flippers, arteries and veins run parallel. Blubber manipulates blood flow to regulate temperature. When it's cold, the blubber constricts vessels to reduce blood flow and conserve heat.

To release excess heat, dolphins rely on thermal windows, areas that lack blubber and are thin and highly vascularized, including the dorsal fin, flukes, and flippers. They also use countercurrent heat exchange. Blood flowing in different directions transfers heat across membranes. So warm blood leaving the heart warms the cold blood returning from the extremities. keeping the core warm while minimizing heat loss to the water. Two pectoral flippers, each with four digits inside. A boneless dorsal fin for stability.

A fluke for propulsion. Though they lack external hind limbs, some individuals have small internal remnants that may contain vestiges of feet and digits. Orcas are notably fast. swimmers, up to 55 kilometers per hour, compared to seals that typically cruise at 9 to 28 kilometers per hour. A study of a Pacific white-sighted dolphin found it could accelerate from 5 meters per second and nearly 9 meters per second and less than a second, using just 5 strokes. The neck vertebrae are fused, which increases stability at high speed, but reduces

flexibility. Most dolphins can't turn their heads. River dolphins, on the other hand, have unfused vertebrae, and can turn their heads up to 90 degrees. Dolphins swim by moving the tail fluke and rear body vertically. Flippers are mainly for steering. All species have a dorsal fin to prevent involuntary spinning. Some dolphins are adapted for deep dives. They can selectively slow their heart rate to conserve oxygen and reroute blood from pressure-tolerant tissues

to the heart, brain, and other vital organs. Hemoglobin and myoglobin store oxygen in body tissues. They have twice as much myoglobin as hemoglobin. Dolphin ears are specially adapted for the marine environment. In humans, the middle ear equalizes the impedance difference between air and the fluid-filled cochlea. Dolphins don't face that problem. There's no great difference between the outer and inner environment. Sound reaches them through the throat, passing through a low impedance, fat-filled cavity to the inner ear.

Air-filled sinus pockets acoustically isolate the ear from skull, improving directional hearing underwater. Dolphins generate sounds independently of breathing, using recycled air that passes through air sacks and structures called faunic lips, sometimes called monkey lips. Eye frequency clicks pass through sound modifying fat bodies, and the melon, a fatty structure in the forehead, the skull of any creature with a melon shows a large depression. This setup enables echolocation for orientation. Most dolphins don't have hair,

but they do have hair follicles that may serve some sensory function. Echo location not only locates objects but also provides information about shape and size, though the exact mechanism isn't fully understood. The small hairs on the rostrum of the Boto, the South American River Dolphin, are thought to function as tactile sensors, possibly compensating for poor eyesight. Dolphin eyes are small relative to body size, but they retain good vision. Eyes placed on the sides of the head give two separate fields of view, rather than the binocular vision humans have.

When dolphins surface, the lens and cornea correct for the near-sightedness caused by water's refraction of light. Eyes contain both rod and cone cells. They see in dim and bright light, but have far more rods than cones. They lack short wavelength-sensitive pigments, meaning color vision is more limited than in most mammals. Most have slightly flattened eyeballs, enlarged pupils that shrink at the surface to prevent damage,

slightly flattened corneas, and atapidum lucidum, reflective tissue behind the retina. all adaptations that let large amounts of light through and produce a very clear image. Glans on the eyelids and outer cornea protect the eye. The olfactory lobes and nerve are absent, suggesting dolphins have no sense of smell. Taste seems similarly limited. Taste buds are atrophied or missing.

Still, some dolphins show preferences. for certain fish, indicating at least some taste ability. Intelligence in dolphins is well documented. They teach, learn, cooperate, and show what looks like grief. The neocortex in many species contains elongated spindle neurons, cells that until 2007 were thought to exist only in great apes and humans. In humans, these neurons, these neurons. are involved in social conduct, emotions, judgment, and theory of mind.

In dolphins, they appear in analogous brain regions, suggesting a similar role. Brain size was once considered a major intelligence indicator. Most of the brain maintains basic bodily functions, so a higher brain-to-body mass ratio may leave more brain available for complex cognition. Allometric analysis shows that mammalian brain size scales at roughly the two-thirds or three-fourths power of body mass. Comparing an animal's actual brain size to the expected size yields an encephalization quotient, another measure of intelligence. Orcas have the second largest brain of any animal after sperm whales.

And some dolphins, a brain-to-body mass ratio, is second only to humans. Self-awareness is considered a marker of advanced abstract thinking, a precursor to processes like thinking about thinking. Research suggests cetaceans possess self-awareness. The most common test is the mirror test. An animal is marked with temporary dye, then shown a mirror. if the animal uses the mirror to examine the mark that's evidence of self-awareness some researchers dispute these findings arguing that the results are open to interpretation and susceptible to the clever hans effect the tendency to see intentional behavior where there may be none the test is less definitive for cetaceans and for primates since primates can touch the mark or the mirror

while cetaceans can only twist and turn to view it. Skeptics suggest behaviors interpreted as self-awareness might just be social responses to another individual. Supporters counter that the behaviors are distinctly different from normal social responses. At 1995, researchers used television to test dolphin's self-awareness, showing dolphins real-time video of themselves, video of another dolphin and recorded footage.

They concluded the evidence suggested self-awareness rather than social behavior. Since then, dolphins have passed the mirror test, though some researchers remain unconvinced. Dolphins are highly social, often living in pods of up to a dozen individuals, though size and structure vary widely by species and local. In areas with abundant food, pods can merge temporarily into super pods that may exceed a thousand dolphins.

Pod membership is fluid, individuals move between groups. They form strong social bonds and will stay with injured or ill members, bringing them to the surface to breathe if needed. This altruism isn't limited to their own species. A dolphin named Moko in New Zealand was observed guiding a stranded pygmy sperm whale and her calf out of shallow water. Dolphins have also been seen protecting human swimmers from sharks, either by swimming in circles around them or charging the sharks. Communication happens through clicks, whistle-like sounds, and other vocalizations. Non-verbal communication includes touch. includes touch and posturing.

Dolphins display culture, something long thought unique to humans and perhaps other primates. In 2005, researchers in Australia found Indo-Pacific bottlenose dolphins teaching their young to use tools. They cover their snouts with sponges to protect them while foraging. This knowledge is mostly passed from mothers to daughters, unlike in primates. where it's generally shared with both sexes. The sponge use is a learned behavior. Dolphins generally sleep with only one brain hemisphere and slow wave sleep at a time, maintaining enough consciousness to breathe and watch for threats.

Earlier sleep stages can occur simultaneously in both hemispheres. In capacity, dolphins sometimes enter a fully asleep state, with both eyes closed and no response to mild stimuli. Respiration becomes automatic. A tail-kick reflex keeps the blowhole above water if necessary. Whether wild dolphins reach this state is unknown. The Indus River dolphin has a different sleep method. Living in water with strong currents and debris,

it must swim continuously to avoid injury, so it sleeps in very short bursts, four to 60 seconds at a time. Bottlenose dolphins have signature whistles, unique sounds that function like names. These whistles identify individuals and are used to communicate over distance. A dolphin develops its signature whistle during its first year and maintains it for life. The development involves vocal production learning, influenced by interactions with other dolphins. Dolphins can address one another by mimicking a specific whistle. Male bottle-nosed whistles tend to resemble their mothers.

Female whistles are more distinctive. Bottlenose dolphins have strong memories for these whistles. They can recognize the signature whistle. of an individual they haven't encountered in over 20 years. Research on signature whistles and other species is limited and has yielded mixed results. Because dolphins traveling groups, communication is essential.

Signal making occurs when similar sounds interfere with the original acoustic signal. In larger groups, individual whistles are less prominent. Dolphins travel in pods that range from a few individuals to many, though they don't necessarily swim close to each other. They stay within the same general area. Higher whistle rates help prevent losing pod members when the group is spread out. Dolphins frequently leap above the water for various reasons. When traveling, jumping saves energy, less friction in the air.

This is called porpoising. Other reasons include orientation, social displays, non-verbal communication, entertainment, and dislodging parasites. In the Port River north of Adelaide, several Indo-Pacific bottlenose dolphins have been seen tailwalking, a highly unusual behavior in the wild. This involves forcing most of the body vertically out of the wild. water and maintaining the position of vigorously pumping the tail, mimicking a standing posture

and moving backward along the water. The behavior started in 1988 when a female named Billy was rescued after becoming trapped in a polluted marina. She spent two weeks recuperating with captive dolphins at a marine park where she observed them tailwalking. After being returned to the port River, she continued performing the behavior. Another dolphin, Wave, copied her. Wave, a very active tail walker, passed the skill to her daughters, Ripple and Pilula. After Billy's early passing, Wave increased her tailwalking, and other dolphins in the group began performing it. By 2011, up to 12 dolphins had been observed tailwalking, though only females appeared to learn it.

In October 2021, a dolphin was observed tailwalking for hours. Scientists find the spread of this behavior through up to two generations surprising, as it brings no apparent advantage and is very energy-consuming. Dolphins can tolerate and recover from a few generations. extreme injuries, though the exact mechanisms aren't known. Even large wounds restore in a way that preserves body shape and affection seems rare. A study published in marine mammal science suggests that at least some dolphins survive shark encounters using sophisticated maneuvers and cooperative tactics.