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15 Delightful Facts About Dolphins

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Dolphins are known for being smart, playful creatures that can learn to perform impressive tricks. But you might not know that dolphins are also champion nappers who have helped the U.S. Navy protect nuclear warheads. We're celebrating National Dolphin Day with these 15 facts about the cute, friendly cetaceans.

1. THEY'RE EXCELLENT NAPPERS.

Since dolphins can't breathe underwater, they need to swim up to the ocean's surface to get air. So how do they sleep without drowning? Essentially, dolphins are champion power nappers. Rather than sleep for several hours at a time, they rest one hemisphere of their brain for 15 to 20 minutes at a time, and they take these "naps" several times each day. By resting one hemisphere of their brain at a time, dolphins can continue swimming, breathing, and watching for predators 24/7.

2. THEY COMMUNICATE WITH CLICKS AND WHISTLES …

dolphins underwater
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Dolphins communicate with one another underwater by making a variety of vocalizations. To find prey and navigate the ocean, they make clicking sounds, and they "speak" to other dolphins by whistling. Dolphins also produce loud burst-pulse sounds when they feel excited or aggressive, such as when they need to scare off a nearby shark. Some female dolphins also produce a burst-pulse to reprimand their offspring, called calves, for bad behavior.

3. … BUT THEIR LANGUAGE REMAINS A MYSTERY.

Although marine scientists have studied and recorded dolphin vocalizations for decades, many aspects of the animals’ language and how they communicate are still unknown. Scientists have not yet broken down the individual units of dolphin sounds, and they're still searching for a Rosetta Stone that links the animals' vocalizations to their behavior. By using new technologies—including algorithms and high-frequency recorders that work underwater—scientists hope to finally unlock the mystery of the dolphin language.

4. THEY USE ECHOLOCATION TO NAVIGATE.

To know where they are in relation to other objects and animals, dolphins use echolocation (a.k.a. biological sonar). After emitting a series of high-pitched clicks, they listen for the echoes to bounce off their surroundings. Based on these echoes, dolphins can judge where they are in space and determine the size and shape of nearby objects. Besides helping dolphins evade predators, echolocation allows them to trap, catch, and eat fish and squid.

5. THEY MAKE FRIENDS WITH OTHER DOLPHINS …

spotted dolphins swimming
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Dolphins are highly social, and scientists are still discovering fascinating details about how the aquatic mammals socialize with one another. In 2015, scientists at Florida Atlantic University's Harbor Branch Oceanographic Institute published research in the Marine Mammal Science journal about the social networks of dolphins. After spending over six years tracking 200 bottlenose dolphins in Florida's Indian River Lagoon, the scientists discovered that dolphins have friends. Instead of spending equal time with the dolphins around them, the animals actually segregate themselves into friend groups. Just like humans, dolphins seem to prefer the company of certain peers more than others.

6. … AND EACH DOLPHIN RESPONDS TO ITS OWN NAME.

Dolphins aren't swimming around with name tags, but every dolphin has its own unique whistle. Scientists believe that dolphins use these signature whistles for life, and female dolphins may even teach their calves their whistles before they're born. Dolphins use their signature whistles to call out to one another and may be able to remember other dolphins' whistles after decades apart.

7. THERE ARE 44 DIFFERENT DOLPHIN SPECIES.

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Although bottlenose dolphins are the most well-known and recognizable, there are 43 other dolphin species. Most species live in temperate and tropical oceans, but a few live in colder oceans or rivers. Depending on their species, dolphins can vary considerably in their physical attributes and behavior. For example, the largest dolphin species, the Orca (also called Killer Whale), can be 30 feet long—10 times longer than the smallest dolphins.

8. THEY DON'T USE THEIR TEETH TO CHEW FOOD.

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Dolphins have teeth, but they don't use their chompers to chew food. Instead, dolphins use their teeth to catch prey (fish, crustaceans, and squid) and swallow it whole. Since they forgo chewing, digestion occurs in their stomach—or, more precisely, in part of their stomach. Dolphins have multiple stomach chambers, one of which is devoted to digestion, while the other chambers store food before it's digested.

9. THEY TYPICALLY GIVE BIRTH TO JUST ONE CALF.

mother and baby dolphin
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Depending on their species, most female dolphins (called cows) carry their babies for nine to 17 months before giving birth to a calf. Interestingly, calves are born tail first, rather than head first, so they don't drown during the birthing process. After nursing for one to two years, a calf typically stays with its mother for the next one to seven years, before mating and having its own calves.

10. THEIR SKIN CAN BE REGENERATED EVERY TWO HOURS.

If you've ever swum with dolphins, you know their skin looks and feels super smooth and sleek. There's a reason for that—a dolphin's epidermis (outer layer of skin) can be sloughed off and replaced with new skin cells as often as every two hours. Because their skin regenerates so often, it stays smooth and, as most scientists believe, reduces drag as they swim.

11. THE U.S. NAVY TRAINS DOLPHINS TO PROTECT NUCLEAR WEAPONS.

A bottlenose dolphin named K-Dog from the Commander Task Unit jumps out of the water in 2003. Commander Task Unit is comprised of special mine clearing teams from The United Kingdom, Australia, and the U.S.
A bottlenose dolphin named K-Dog from the Commander Task Unit jumps out of the water in 2003. Commander Task Unit is comprised of special mine clearing teams from The United Kingdom, Australia, and the U.S.
Brien Aho, U.S. Navy/Getty Images

Despite dolphins' general friendliness, some of them are trained for combat. The Navy Marine Mammal Program at San Diego's Space and Naval Warfare Systems Command (SPAWAR) trains dozens of bottlenose dolphins (as well as sea lions) to help the U.S. Navy. In the past, the U.S. military has used dolphins in conflicts in Vietnam and the Persian Gulf. Today, thanks to their intelligence, speed, and echolocation skills, dolphins are trained to find enemy swimmers, locate underwater mines, and guard nuclear arsenals.

12. THEY'RE NOT THE SAME AS PORPOISES.

To the untrained eye, dolphins and porpoises look nearly identical, and many people mistakenly think that porpoises are a type of dolphin. But the two species belong to completely different families and differ in their physical attributes. So how can you tell them apart? Dolphins, which are usually bigger than porpoises, typically have longer beaks and curved dorsal fins. Porpoises, on the other hand, have more triangular dorsal fins as well as spade-shaped (rather than conical) teeth.

13. HUNTING, OVERFISHING, AND RISING OCEAN TEMPERATURES THREATEN THEM.

Some dolphin species are endangered or functionally extinct (like China's baiji dolphin) due to hunting, overfishing, and pollution. Although dolphin meat is high in mercury, the animals are still hunted for their meat and eaten in parts of Japan and the Faroe Islands of Denmark. Overfishing means that dolphins' food sources are shrinking, and some dolphins get caught up in fishing nets and die. Additionally, climate change and rising ocean temperatures are driving some fish and squid away from their natural habitats, putting dolphins' main food source at risk.

14. A SUPERPOD CAN CONSIST OF MORE THAN 1000 DOLPHINS.

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Dolphins live in groups, called pods, that typically contain dozens or hundreds of dolphins. By swimming in a pod, dolphins work together to hunt prey, evade predators, and care for sick or injured members. But different pods can also merge, forming a superpod of more than 1000 dolphins. Superpods are typically temporary and occur in parts of the ocean with plentiful food (and less competition for tasty squid).

15. THE OLDEST DOLPHIN IN CAPTIVITY LIVED TO 61 YEARS OLD.

Dolphin lifespan varies greatly by species. Most dolphins in the wild live for a few decades, while those in captivity have a drastically reduced lifespan and may live for only a few years. So it's all the more shocking that the oldest dolphin in captivity lived to be a sexagenarian. Nellie, a bottlenose dolphin who lived in a marine entertainment park in Florida, was born in 1953. She appeared on TV shows and commercials and performed tricks for the park's attendees before passing away in 2014.

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Scientific Reports, Fernando Ramirez Rozzi
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Stones, Bones, and Wrecks
Humans Might Have Practiced Brain Surgery on Cows 5000 Years Ago
Scientific Reports, Fernando Ramirez Rozzi
Scientific Reports, Fernando Ramirez Rozzi

In the 1970s, archaeologists discovered a site in France containing hundreds of cow skeletons dating back 5000 to 5400 years. The sheer number wasn't surprising—human agriculture in that part of the world was booming by 3000 BCE. What perplexed scientists was something uncovered there a few decades later: a cow skull bearing a thoughtfully drilled hole. Now, a team of researchers has released evidence that suggests the hole is an early example of animal brain surgery.

Fernando Ramírez Rozzi, a paleontologist with the French National Center for Scientific Research, and Alain Froment, an anthropologist at the Museum of Mankind in Paris, published their findings in the journal Nature Scientific Reports. After comparing the opening to the holes chiseled into the skulls of humans from the same era, they found the bones bore some striking similarities. They didn't show any signs of fracturing from blunt force trauma; rather, the hole in the cow skull, like those in the human skulls, seemed to have been carved out carefully using a tool made for exactly that purpose. That suggests that the hole is evidence of the earliest known veterinary surgery performed by humans.

Trepanation, or the practice of boring holes into human skulls, is one of the oldest forms of surgery. Experts are still unsure why ancient humans did this, but the level of care that went into the procedures suggests that the surgery was likely used to treat sick patients while they were still alive. Why a person would perform this same surgery on a cow, however, is harder to explain.

The authors present a few theories, the first being that these ancient brain surgeons were treating a sick cow the same way they might treat a sick human. If a cow was suffering from a neural disease like epilepsy, perhaps they though that cutting a hole in its head would relieve whatever was agitating the brain. The cow would have needed to be pretty special to warrant such an effort when there were hundreds of healthy cows living on the same plot of land, as evidenced by the skeletons it was found with.

Another possible explanation was that whoever operated on the cow did so as practice to prepare them for drilling into the heads of live humans one day. "Cranial surgery requires great manual dexterity and a complete knowledge of the anatomy of the brain and vessel distribution," the authors write in the study. "It is possible that the mastery of techniques in cranial surgery shown in the Mesolithic and Neolithic periods was acquired through experimentation on animals."

Either way, the bovine patient didn't live to see the results of the procedure: The bone around the hole hadn't healed at all, which suggests the cow either died during surgery or wasn't alive to begin with.

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Animals
15 Incredible Facts About Pigeons
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Though they're often described as "rats with wings" (a phrase popularized by the movie Stardust Memories), pigeons are actually pretty cool. From homing instincts to misleading rump feathers, here are 15 things you might not know about these avian adventurers.

1. THEY MIGHT BE THE FIRST DOMESTICATED BIRD.

The common city pigeon (Columba livia), also known as the rock pigeon, might be the first bird humankind ever domesticated. You can see them in art dating back as far as 4500 BCE in modern Iraq, and they've been a valuable source of food for thousands of years.

2. THEY WON OVER CHARLES DARWIN—AND NIKOLA TESLA.

Pigeon-breeding was a common hobby in Victorian England for everyone from well-off businessmen to average Joes, leading to some fantastically weird birds. Few hobbyists had more enthusiasm for the breeding process than Charles Darwin, who owned a diverse flock, joined London pigeon clubs, and hobnobbed with famous breeders. Darwin's passion for the birds influenced his 1868 book The Variation of Animals and Plants Under Domestication, which has not one but two chapters about pigeons (dogs and cats share a single chapter).

Nikola Tesla was another great mind who enjoyed pigeons. He used to care for injured wild pigeons in his New York City hotel room. Hands down, Tesla's favorite was a white female—about whom he once said, "I loved that pigeon, I loved her as a man loves a woman and she loved me. When she was ill, I knew and understood; she came to my room and I stayed beside her for days. I nursed her back to health. That pigeon was the joy of my life. If she needed me, nothing else mattered. As long as I had her, there was a purpose in my life." Reportedly, he was inconsolable after she died.

3. THEY UNDERSTAND SPACE AND TIME.

In a 2017 Current Biology study, researchers showed captive pigeons a series of digital lines on a computer screen for either two or eight seconds. Some lines were short, measuring about 2.3 inches across; others were four times longer. The pigeons were trained to evaluate either the length of the line or how long it was displayed. They found that the more time a line was displayed, the longer in length the pigeon judged it to be. The reverse was true too: If the pigeons encountered a longer line, they thought it existed in time for a greater duration. Pigeons, the scientists concluded, understand the concepts of both time and space; the researchers noted "similar results have been found with humans and other primates."

It's thought that humans process those concepts with a brain region called the parietal cortex; pigeon brains lack that cortex, so they must have a different way of judging space and time.

4. THEY CAN FIND THEIR WAY BACK TO THE NEST FROM 1300 MILES AWAY.

A pigeon flying in front of trees.
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The birds can do this even if they've been transported in isolation—with no visual, olfactory, or magnetic clues—while scientists rotate their cages so they don't know what direction they're traveling in. How they do this is a mystery, but people have been exploiting the pigeon's navigational skills since at least 3000 BCE, when ancient peoples would set caged pigeons free and follow them to nearby land.

Their navigational skills also make pigeons great long-distance messengers. Sports fans in ancient Greece are said to have used trained pigeons to carry the results of the Ancient Olympics. Further east, Genghis Khan stayed in touch with his allies and enemies alike through a pigeon-based postal network.

5. THEY SAVED THOUSANDS OF HUMAN LIVES DURING WORLD WARS I AND II.

Pigeons' homing talents continued to shape history during the 20th century. In both World Wars, rival nations had huge flocks of pigeon messengers. (America alone had 200,000 at its disposal in WWII.) By delivering critical updates, the avians saved thousands of human lives. One racing bird named Cher Ami completed a mission that led to the rescue of 194 stranded U.S. soldiers on October 4, 1918.

6. TWO PIGEONS ALMOST DISTRACTED FROM THE DISCOVERY OF EVIDENCE OF THE BIG BANG.

In 1964, scientists in Holmdel, New Jersey, heard hissing noises from their antenna that would later prove to be signals from the Big Bang. But when they first heard the sound, they thought it might be, among other things, the poop of two pigeons that were living in the antenna. "We took the pigeons, put them in a box, and mailed them as far away as we could in the company mail to a guy who fancied pigeons," one of the scientists later recalled. "He looked at them and said these are junk pigeons and let them go and before long they were right back." But the scientists were able to clean out the antenna and determine that they had not been the cause of the noise. The trap used to catch the birds (before they had to later be, uh, permanently removed) is on view at the Smithsonian Air & Space Museum.

7. YOU CAN TRAIN THEM TO BE ART SNOBS …

Japanese psychologist Shigeru Watanabe and two colleagues earned an Ig Nobel Prize in 1995 for training pigeons, in a lab setting, to recognize the paintings of Claude Monet and Pablo Picasso and to distinguish between the painters. The pigeons were even able to use their knowledge of impressionism and cubism to identify paintings of other artists in those movements. Later, Watanabe taught other pigeons to distinguish watercolor images from pastels. And in a 2009 experiment, captive pigeons he'd borrowed were shown almost two dozen paintings made by students at a Tokyo elementary school, and were taught which ones were considered "good" and which ones were considered "bad." He then presented them with 10 new paintings and the avian critics managed to correctly guess which ones had earned bad grades from the school's teacher and a panel of adults. Watanabe's findings indicate that wild pigeons naturally categorize things on the basis of color, texture, and general appearance.

8. … AND TO DISTINGUISH WRITTEN WORDS.

In a 2016 study, scientists showed that pigeons can differentiate between strings of letters and actual words. Four of the birds built up a vocabulary of between 26 and 58 written English words, and though the birds couldn't actually read them, they could identify visual patterns and therefore tell them apart. The birds could even identify words they hadn't seen before.

9. FLUFFY PIGEON FEET MIGHT ACTUALLY BE PARTIAL WINGS.

A white pigeon with curly feathers and fluffy feet.
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A few pigeon breeds have fuzzy legs—which hobbyists call "muffs"—rather than scaly ones. According to a 2016 study, the DNA of these fluffy-footed pigeons leads their hind legs to take on some forelimb characteristics, making muffed pigeon legs look distinctly wing-like; they're also big-boned. Not only do they have feathers, but the hindlimbs are somewhat big-boned, too. According to biologist Mike Shapiro, who led the study, "pigeons' fancy feathered feet are partially wings."

10. SOME PIGEONS DISTRACT FALCONS WITH WHITE RUMP FEATHERS.

In a life-or-death situation, a pigeon's survival could depend upon its color pattern: Research has shown that wild falcons rarely go after pigeons that have a white patch of feathers just above the tail, and when the predators do target these birds, the attacks are rarely successful.

To figure out why this is, Ph.D. student Alberto Palleroni and a team tagged 5235 pigeons in the vicinity of Davis, California. Then, they monitored 1485 falcon-on-pigeon attacks over a seven-year span. The researchers found that although white-rumped pigeons comprised 20 to 25 percent of the area's pigeon population, they represented less than 2 percent of all the observed pigeons that were killed by falcons; the vast majority of the victims had blue rumps. Palleroni and his team rounded up 756 white- and blue-rumped pigeons and swapped their rump feathers by clipping and pasting white feathers on blue rumps, and vice versa. The falcons had a much easier time spotting and catching the newly blue-rumped pigeons, while the pigeons that received the white feathers saw predation rates plummet.

Close observation revealed that the white patches distract birds of prey. In the wild, falcons dive-bomb other winged animals from above at high speeds. Some pigeons respond by rolling away in midair, and on a spiraling bird, white rump feathers can be eye-catching, which means that a patch of them may divert a hungry raptor's focus long enough to make the carnivore miscalculate and zip right past its intended victim.

11. DODOS WERE RELATED TO TODAY'S PIGEONS.

Two blue and green Nicobar pigeons.
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Though most of this list focuses on the rock pigeon, there are 308 living species of pigeons and doves. Together, they make up an order of birds known as the columbiformes. The extinct dodo belonged to this group as well.

Flightless and (somewhat) docile, dodos once inhabited Mauritius, an island near Madagascar. The species had no natural predators, but when human sailors arrived with rats, dogs, cats, and pigs, it began to die out, and before the 17th century came to a close, the dodo had vanished altogether. DNA testing has confirmed that pigeons are closely related to the dodo, and the vibrant Nicobar pigeon (above) is its nearest genetic relative. A multi-colored bird with iridescent feathers, this near-threatened creature is found on small islands in the South Pacific and off Asia. Unlike the dodo, it can fly.

12. AT ONE POINT, MORE THAN ONE-QUARTER OF ALL THE BIRDS LIVING IN THE U.S. MAY HAVE BEEN PASSENGER PIGEONS.

Wild/feral rock pigeons reside in all 50 states, which makes it easy to forget that they're invasive birds. Originally native to Eurasia and northern Africa, the species was (most likely) introduced to North America by French settlers in 1606. At the time, a different kind of columbiform—this one indigenous—was already thriving there: the passenger pigeon (Ectopistes migratorius). As many as 5 billion of them were living in America when England, Spain, and France first started colonizing, and they may have once represented anywhere from 25 to 40 percent of the total U.S. bird population. But by the early 20th century, they had become a rare sight, thanks to overhunting, habitat loss, and a possible genetic diversity issue. The last known passenger pigeon—a captive female named Martha—died on September 1, 1914.

13. THEY'RE REALLY GOOD AT MULTITASKING.

According to one study, they're more efficient multitaskers than people are. Scientists at Ruhr-Universitat Bochum put together a test group of 15 humans and 12 pigeons and trained all of them to complete two simple jobs (like pressing a keyboard once a light bulb came on). They were also put in situations wherein they'd need to stop working on one job and switch over to another. In some trials, the participants had to make the change immediately. During these test runs, humans and pigeons switched between jobs at the same speed.

But in other trials, the test subjects were allowed to complete one assignment and then had to wait 300 milliseconds before moving on to the next job. Interestingly, in these runs, the pigeons were quicker to get started on that second task after the period ended. In the avian brain, nerve cells are more densely packed, which might enable our feathered friends to process information faster than we can under the right circumstances.

14. PIGEONS PRODUCE FAKE "MILK."

Only mammals produce genuine milk, but pigeons and doves (along with some other species of birds) feed their young with something similar—a whitish liquid filled with nutrients, fats, antioxidants, and healthy proteins called "crop milk." Both male and female pigeons create the milk in the crop, a section of the esophagus designed to store food temporarily. As is the case with mammal milk, the creation of crop milk is regulated by the hormone prolactin. Newly-hatched pigeons drink crop milk until they're weaned off it after four weeks or so. (And if you've ever asked yourself, "Where are all the baby pigeons?" we have the answer for you right here.)

15. ONE STUDY SUGGESTS THAT, GIVEN THE RIGHT CONDITIONS, THEY'RE AS GOOD AT IDENTIFYING CANCER AS DOCTORS.

We've already established that pigeons are excellent at differentiating between artists and words, but a 2015 study revealed they can also distinguish between malignant and benign growths in the right conditions. Researchers at University of California Davis Medical Center put 16 pigeons in a room with magnified biopsies of potential breast cancers. If the pigeons correctly identified them as either benign or malignant, they got a treat, According to Scientific American.

"Once trained, the pigeons' average diagnostic accuracy reached an impressive 85 percent. But when a "flock sourcing" approach was taken, in which the most common answer among all subjects was used, group accuracy climbed to a staggering 99 percent, or what would be expected from a pathologist. The pigeons were also able to apply their knowledge to novel images, showing the findings weren't simply a result of rote memorization."

Mammograms proved to be more of a challenge, however; the birds could memorize signs of cancer in the images they were trained on but could not identify the signs in new images.

No matter how impressive their results, "I don't anticipate that pigeons, no matter how good they become at pathology or radiology, will be playing a role in actual patient care—certainly for the foreseeable future," study co-author Richard M. Levenson told Scientific American. "There are just too many regulatory barriers—at least in the West."

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