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.

an orca jumping out of the water
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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.

two smiling dolphins
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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.

a pod of dolphins swimming
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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.

Want to Give a Retired Police or Military Dog a Forever Home? Mission K9 Rescue Can Help

Mission K9 Rescue
Mission K9 Rescue

Over the course of their careers, working dogs perform lifesaving duties while assisting members of the police force and military. These dogs receive a lot of appreciation while they're on the job, but as they enter retirement, they're often forgotten in animal shelters. An organization called Mission K9 Rescue is dedicated to placing these dogs in loving forever homes after they've served the United States.

"Our mission is to give K9 veterans—and other working dogs who have served our country—safe, peaceful, and loving homes upon retirement from service," K9 co-founder and president Kristen Maurer tells Mental Floss. "There are so many animal-loving patriots in America, and most don't realize that many of these brave, selfless dogs often remain overseas much longer than needed when they are no longer able to work. Some do not receive adequate care. We bring awareness of their plight to the public, and we work tirelessly to rescue, reunite, re-home, rehabilitate, and repair these dogs so they can live out the rest of their days in a safe and comfortable environment."

Many retired dogs are abandoned in kennels—both in the U.S. and abroad—but for some, the situation is even more severe. According to Mission K9 Rescue, working dogs are sometimes euthanized en masse when they can no longer do their jobs. The organization aims not only to remove these dogs from harm's way, but to find them forever families that are a perfect fit for them.

After rescuing dogs from both the U.S. and overseas, Mission K9 Rescue matches them with new owners. If the dog has a past handler who is interested in adopting them permanently, reuniting the pair is a priority. For all other cases, the organization goes through a rigorous process to find dogs a brand-new home.

Mission K9 also specializes in rehabilitating dogs who have suffered either mental trauma or physical injuries in their work. Just like humans, canines can develop PTSD from working in stressful, high-pressure situations. After they're rescued, animals are given as much time as they need to decompress and reintegrate into society before they're adopted. On top of the mental demands, being a working dog causes physical strain, and Mission K9 provides medical care to dogs with injuries and other issues.

Anyone can apply to adopt a retired working dog from Mission K9 Rescue. If you're interested in bringing one into your home, you can fill out the application on the group's website.

German shepherd in a bed at home.
Mission K9 Rescue

Two dogs in the backseat of a car.
Mission K9 Rescue

Dog and owner in front of home.
Mission K9 Rescue

Some Fish Eggs Can Hatch After Being Pooped Out by Swans

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iStock/olaser

A question that’s often baffled scientists is how certain species of fish can sometimes appear—and even proliferate—in isolated bodies of water not previously known to harbor them. A new study has demonstrated that the most unlikely explanation might actually be correct: It’s possible they fell from the sky.

Specifically, from the rear end of a swan.

A study in the journal Ecology by researchers at the Unisinos University in Brazil found that killifish eggs can, in rare cases, survive being swallowed by swans, enduring a journey through their digestive tracts before being excreted out. This kind of fecal public transportation system explains how killifish can pop up in ponds, flood waters, and other water bodies that would seem an unlikely place for species to suddenly appear.

After discovering that some plants could survive being ingested and then flourish in swan poop, researchers took notice of a killifish egg present in a frozen fecal sample. They set about mixing two species of killifish eggs into the food supply of coscoroba swans living in a zoo. After waiting a day, they collected the poop and dug in looking for the eggs.

Of the 650 eggs they estimated to have been ingested by the swans, about five were left intact. Of those, three continued to develop. Two died of a fungal infection, but one survived, enduring 30 hours in the gut and hatching 49 days after being excreted.

Because killifish eggs have a thick outer membrane, or chorion, they stand a chance of coming through the digestive tract of an animal intact. Not all of what a swan ingests will be absorbed; their stomachs are built to extract nutrients quickly and get rid of the whatever's left so the birds can eat again. In rare cases, that can mean an egg that can go on to prosper.

Not all fish eggs are so durable, and not all fish are quite like the killifish. Dubbed the "most extreme" fish on Earth by the BBC, killifish have adapted to popping up in strange environments where water may eventually dry up. They typically live for a year and deposit eggs that can survive in soil, delaying their development until conditions—say, not being inside a swan—are optimal. One species, the mangrove killifish, can even breathe through its skin. When water recedes, they can survive on land for over two months, waddling on their bellies or using their tails to "jump" and eat insects. A fish that can survive on dry land probably doesn't sweat having to live in poop.

The researchers plan to study carp eggs next to see if they, too, can go through a lot of crap to get to where they’re going.

[h/t The New York Times]

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