Our Most Interesting Facts About Animals

Koala Fingerprints Are Almost Indistinguishable From Those of Humans

Every fingerprint is unique, but that doesn’t mean they’re easy to tell apart — especially since humans aren’t the only species that’s developed them. Chimpanzees and gorillas have fingerprints too, but it’s actually koalas — far more distant on the evolutionary tree from humans — whose prints are most similar to our own. This was first discovered by researchers at the University of Adelaide in Australia in 1996, one of whom went so far as to joke that “although it’s extremely unlikely that koala prints would be found at the scene of a crime, police should at least be aware of the possibility.”

That discovery lent support to one of the primary theories in the centuries-long debate over the purpose of fingerprints and their swirly microscopic grooves: They help grasp. Koalas’ survival depends on their ability to climb small branches of eucalyptus trees and grab their leaves to eat, so the fact that they developed fingerprints — which assist in that action — independently of primates millions of years ago is likely no coincidence.

Some Bats Sing Love Songs

Anyone who’s ever serenaded their sweetheart has more in common with bats than they might think. In 2009, researchers at the University of Texas at Austin and Texas A&M studied the vocalizations of Tadarida brasiliensis — the Brazilian free-tailed bat, more commonly known as the Mexican free-tailed bat — and found the tunes to be surprisingly nuanced love songs. Though difficult for humans to hear, the songs consist of unique syllables that combine to form three types of “phrases”: chirps, buzzes, and trills. The males combine these phrases in different ways to attract females — and to warn other males to stay away.

What makes this especially remarkable is that, until recently, bats weren’t thought to communicate with one another in such a structured way. But when the researchers listened to recordings of two free-tailed colonies in Austin and College Station, Texas, they discovered that they “use the same ‘words’ in their love phrases,” according to lead researcher Kirsten Bohn.

Cats Can Be Allergic to People

If you love cats but can’t have one of your own because you’re allergic, the feeling may be mutual. It isn’t common, but cats can be allergic to people. The condition is rare in part because we humans usually bathe regularly and thus don’t shed as much dead skin or hair as other animals (and it’s somewhat unclear how much of a problem human dander may be for felines). That said, cats are fairly sensitive to chemicals and sometimes have a negative reaction to certain perfumes, laundry detergents, and soaps. Cat allergic reactions look much the same as the ones humans get — they may manifest as sneezing, runny noses, rashes, hives, or other uncomfortable symptoms. In rare cases, cats can even be allergic to dogs. (Maybe that’s why some of them don’t get along.)

The Pattern of Every Tiger’s Stripes Is Unique

Not unlike human fingerprints, the pattern of every tiger’s stripes is one of a kind. And though those markings are invariably beautiful, they aren’t just for decoration. Biologists refer to tiger stripes as an example of disruptive coloration, as their vertical slashes help them hide in plain sight by breaking up their shape and size so they blend in with tall grass, trees, and other camouflage-friendly environments. Tigers are solitary hunters who ambush their prey, so the ability to remain undetected while on the hunt is key to their survival. Markings also differ among subspecies, with Sumatran tigers having the narrowest stripes and Siberian tigers having fewer than the rest of their big cat brethren.

Norway Once Knighted a Penguin

Before he was a knight, Sir Nils Olav was a king — king penguin, that is. The flightless seabird was made both mascot and an honorary member of the Norwegian King’s Guard after the battalion visited the Edinburgh Zoo in 1972 and Major Nils Egelien had the idea to adopt a penguin. Sir Nils (he’s named for both Egelien and former King of Norway Olav V) quickly ascended through his country’s military ranks, receiving a promotion each time the King’s Guard returned to the zoo around performances for the Edinburgh Military Tattoo. The 2008 knighthood took place before 130 guardsmen and a crowd of several hundred people, during which King Harald V of Norway read out a citation describing Sir Nils as a penguin “in every way qualified to receive the honor and dignity of knighthood.” The penguin knighted in 2008 wasn’t the original Nils Olav, however. He was preceded by two others, inheriting their name and title when they went to the great penguin colony in the sky. (Penguins often live about 15 to 20 years, though some king penguins can live over 40 years in captivity.)

Ravens Can Remember Human Faces

Ravens are smart — really smart. Studies have shown that they can use tools, remember human faces, and even plan for the future. This behavior cuts both ways for humans: Edgar Allan Poe’s favorite birds have demonstrated a tendency to both favor people who show them kindness and hold grudges against those who treat them poorly. These preferences aren’t fleeting, either — they may last for years.

Raven intelligence is comparable in some cases to that of chimpanzees, which are among the smartest members of the animal kingdom. What’s more, they aren’t the only ones upending the “bird brain” stereotype: Other members of the corvid family — namely crows, jays, and magpies — have displayed exceptional intelligence as well. So the next time you encounter a raven, be sure you get on its good side. You may make a new friend who won’t forget you anytime soon.

Reindeer Eyes Change Color — They’re Golden in Summer and Blue in Winter

Rudolph’s nose may have been red, but his eyes were blue — except in the summer, when they would have been golden. That’s because reindeer eyes change color depending on the time of year, which helps them see better in different light levels. Their blue eyes are approximately 1,000 times more sensitive to light than their golden counterparts, a crucial adaptation in the dark days of winter. Only one part changes color, however: the tapetum lucidum, a mirrored layer situated behind the retina. Cats have it, too — it’s why their eyes appear to glow in the dark. This part of the reindeer retina shines a different hue depending on the season.

There Is a Dedicated “Air Horse One” Airplane for Transporting Horses

Just because horses are fast doesn’t mean they’re easy to transport. Often weighing more than 1,000 pounds and not exactly quick to do things they aren’t inclined to, our equine friends nevertheless often need to be brought from point A to point B. Luckily, there’s a plane dedicated to ferrying horses, known as (what else?) Air Horse One. Owned and operated by Tex Sutton Equine Air Transportation, it’s a Boeing 727-200 cargo aircraft used for race horses, show horses, and other VIP clients. As such, tickets don’t run cheap — one-way trips can set you back $5,000.

It would appear to be worth it, however. Everything about the trip in general and the plane in particular is tailored to its passengers’ needs, from custom-built ramps and padded stalls to smooth rides that avoid steep ascents, descents, and adverse weather conditions. Air Horse One also focuses on direct flights to shorten travel times, since Appaloosas and Clydesdales dislike layovers as much as the rest of us. In lieu of carry-on bags, some horses even get to bring along “pets,” such as goats, to keep them company. We should all be so lucky.

All Clownfish Are Born Male

There’s a good reason why both main characters in Finding Nemo are male, at least initially. All clownfish are born that way, and it’s only when a group’s dominant female dies or disappears that a male will develop into a female and become the new matriarch. All clownfish have the ability to turn female, and the change is permanent once it occurs. The transformation begins almost immediately after the dominant female leaves, and starts in the brain before manifesting itself in the sex organs. Had the beloved Pixar film been devoted to scientific accuracy, Nemo’s father, Marlin, might not have been just his sole caregiver after tragedy befell the boy’s mother — he might literally have become his mother.

Clownfish aren’t the only reef-dwellers that can change sex. Researchers have identified no fewer than 500 fish species capable of doing so; some, like the coral-dwelling species of gobies, can even switch back and forth. The process is believed to have reproductive benefits, as it allows a single fish to reproduce as both sexes throughout its life.  

The World’s Only Egg-Laying Mammals Live in Australia and New Guinea

There are around 6,500 currently recognized species of mammals, and all but five of them give birth to live young. The five exceptions, known as monotremes, are found exclusively in Australia and New Guinea. The platypus is the best known of these, while four living species of echidna round out the list: short-beaked, western long-beaked, eastern long-beaked, and Sir David’s. Monotremes live fairly typical mammalian lives once they’ve hatched, including being nursed by their mothers’ milk.

Male Nightingales Advertise Their Skills as Fathers Through Song

If you know anything about nightingales, it’s probably that they sing. Written about by the likes of ancient Greek playwright Aristophanes and English poet John Keats, they’ve also inspired such composers as Beethoven and Stravinsky to pay homage to their melancholy warbling. But not all of their songs are mournful: In fact, male nightingales use some of them to advertise their skills as fathers. One of the many factors female nightingales consider when assessing prospective mates is their suitors’ paternal potential, and a 2015 study on the subject showed that better male nightingale singers are known to feed their children more often than their less-talented peers. “Better” here means singing in a more orderly fashion — repeating the same song types over and over — and varying their song choices, with plenty of buzzes, trills, and whistles.

Whereas it was previously thought that the size of a male’s repertoire was the sole criterion a female considered, in nightingales, the kind of song is crucial as well. Overall, male nightingales are known to be doting fathers — they visit their chicks’ nest as many as 16 times every hour, which is about as often as their mothers do.

Goats Have Rectangular Pupils

The animal kingdom is full of incredible variety, thanks to evolution, but one thing most animals have in common is that they use a set of eyes to navigate the world around them. For mammals, one big factor determining the shape of a pupil is whether the creature is predator or prey. For example, a goat is a grazing prey animal that would be a pretty easy target for coyotes, bears, and other predators with sharp teeth. Yet evolution gave the goat a few tools to defend itself. The horns certainly help, but the biggest advantage is a goat’s horizontal rectangular pupils. These long, horizontal pupils create a panoramic view that lets the animal see more of the landscape, which makes it harder to sneak up on them. The pupils also enhance the image quality of objects (read: threats) all around the goats, and they cut down on glare from the sky by capturing less light from above and more from below. Cats and snakes, on the other hand, are ambush predators, whose vertical pupils help them hunt in the night and judge the distance between themselves and their next meal. But according to scientists, vertical pupils are reserved only for animals whose eyes are close to the ground. That’s why other cats that are higher up, like lions and tigers, have round pupils rather than vertical ones.

Hummingbirds Can See Colors That Humans Can’t

Colorblindness is relative. Just as we can perceive hues that dogs can’t, hummingbirds can see colors that humans can’t. Whereas the three types of color-sensitive cone cells in our eyes allow us to see red, green, and blue light, hummingbirds (and most other birds) have a fourth type of cone attuned to ultraviolet light. In addition to UV light, birds may even be able to see combination colors like ultraviolet+green and ultraviolet+red — something we mere humans can only imagine.

Being able to see this way is especially useful for hummingbirds, whose endless quest for sugar is aided by their ability to discern different-colored flowers — including “nonspectral” colors that combine hues from widely different parts of the color spectrum. Purple is the only nonspectral color we humans can perceive (it involves both blue and red, or both short and long wavelengths of light), but some birds might see as many as five: purple, ultraviolet+red, ultraviolet+green, ultraviolet+yellow, and ultraviolet+purple. That certainly sounds worth singing about.

Rats Bop Their Heads in Time to Music

Most rats live their lives entirely unseen by humans. As kings of the background, they often scurry through human environments just out of sight or after dark, looking for leftover morsels. But researchers believe rats might not just be picking up our food crumbs — they could also be picking up on the beats in our music. A study published in 2022 suggests rats may have a humanlike sense of rhythm, which they express by bopping their heads to the beat. Scientists once believed that few animals were beat-sensitive (aside from some birds), but rats exposed to music made microscopic head movements that were picked up by tiny, wireless motion detectors. The researchers hypothesized that rats would prefer faster jams thanks in part to their rapid heartbeats, though surprisingly, lab rats synced up best with music in the 120 to 140 beats-per-minute range — just like humans.

South Florida Is the Only Region Where Both Alligators and Crocodiles Coexist in the Wild

Alligators and crocodiles have a lot in common. They’re both beefy reptiles with a serious set of teeth and strong Triassic vibes. However, there are some big differences between them: Alligators usually have a more U-shaped snout, whereas crocodiles sport a more V-shaped schnoz; alligators stick to fresh water, while crocodiles live in salty environments; alligators are blacker, while crocs prefer earth tones like brown. However, the biggest difference is usually in the locations these two gargantuan reptiles call home. American crocodiles (Crocodylus acutus) can be found in Cuba, Jamaica, southern Mexico, Central America, Ecuador, and elsewhere. Meanwhile, the American alligator (Alligator mississippiensis) mostly sticks to the southeastern U.S. You’ll likely never be tasked with differentiating the two creatures in the wild — that is, unless you find yourself in south Florida.

On the tip of the Florida peninsula lies the U.S.’s third-largest national park — the Everglades. It’s here that the southern extreme of the American alligator’s range overlaps with the northern extreme of the American crocodile’s range. The 7,800-square-mile expanse of wetlands has both brackish and saltwater environments that create a perfect home for crocs, while fresh water supplied by lakes, rivers, and rainfall provides the preferred habitat for alligators.

Monkeys Have Been Using Stone Tools for Thousands of Years

Humans are often thought of as the smartest animals, and one of the perks of our top-notch brains (with a little help from our opposable thumbs) is supposedly that we’re the only species that can use tools. That’s what we used to think, anyway. Archaeologists analyzing a site in Brazil’s Serra da Capivara National Park discovered that capuchin monkeys had used rounded quartzite stones to smash open cashew husks against tree roots or stone “anvils.” After digging through layers of sediment in four phases of excavation, the scientists found stone tools that had been used by the capuchins dating back around 3,000 years.

The researchers also found signs that the monkeys’ tool use had changed over time — the creatures first used smaller stone tools, and then around 560 years ago, switched to larger ones, which may have meant they were eating harder foods, according to National Geographic. This evolution could have occurred due to different groups of capuchins moving into the area, or a change in the local plants. Either way, the study marked the first time such an evolution in tool use had been seen in a nonhuman species. Scientists suspect that further exploration of this site, and others like it, could give an unprecedented look at humanity’s own tool-use evolution, which began millions of years ago.

Male Squirrels Get Smarter in the Fall

Autumn heralds the arrival of many things: pumpkin pie, crisp morning air, and, apparently, more intelligent rodents. Male squirrels get smarter in the fall due to their hippocampus (a part of the brain involved in memory) increasing in size during the caching season — the time of year when they gather even more nuts than usual. (In an especially adorable move, they stuff their snacks in their cheeks before moving their food to a more permanent storage spot.) Interestingly, female squirrel brains don’t show the same effect; researchers speculate that male squirrel brains may change in the fall to act more like the females’ brains already function all year long. The slightly bigger brains may help male squirrels remember exactly where they’ve stored their nuts, although scientists are still teasing out how.

Rats Giggle When Tickled

It is sometimes said that there are two types of tickling: knismesis and gargalesis. The former is the “light, feather-like” kind, which doesn’t induce laughter, while the latter is more high-pressure and does cause laughter. And while you may think of humans as the only creatures susceptible to gargalesis, one of our much smaller counterparts is as well: the humble rat. Rats actually love being tickled, especially on their back and belly, and there’s even a specific term for the frolicking they do in between tickles: freudensprünge, or “joy jumps.” Sadly, rat giggles are too high for us to hear without special microphones that can reproduce the sound in a lower register. (That doesn’t make videos of rats being tickled any less adorable, however.)

Crocodiles Can’t Stick Out Their Tongues

The jaws of a crocodile are an amazing specimen of evolution. With a second jaw joint unlike anything found in mammals, a crocodile can spread the force of its tremendous bite throughout its mouth. In fact, crocodiles have the most powerful chomp in the animal kingdom, at 3,700 pounds per square inch for a saltwater crocodile — 30 times the force of a human bite. But that’s not the only interesting thing about a crocodile’s mouth: Their tongues are incapable of getting between those devastating jaws thanks to being permanently rooted to the floor of their mouths. Their tongues are also held in place by a membrane attached to the roof in the back of the mouth, which keeps the throat closed when the crocodile is submerged.

Whale Sharks Have Tiny Teeth on Their Eyeballs

One of the strangest attributes of any eyeball on Earth belongs to the whale shark (Rhincodon typus). Because these gentle giants of the sea don’t have eyelids to protect their organs of sight, they’ve developed thousands of tiny teeth known as “dermal denticles” to fend off any potentially vision-damaging elements the ocean might throw at them, whether it’s items drifting in the sea or biochemical hazards. In 2020, scientists in Japan discovered the denticles when analyzing both dead and living sharks, and estimated that each eye could have as many as nearly 3,000 of these tiny teeth. When viewed under a microscope, the denticles resemble the shape of an oak leaf, but much smaller.

Dermal denticles are commonly found on many shark species’ skin, acting like scales that cut down on turbulence and drag when gliding through the water. However, the whale shark is the only species in whom these denticles congregate around the iris. This scale-like armor, combined with the whale shark’s unique ability to retract its eyes into its sockets, has scientists reexamining the importance of a whale shark’s vision. For years, scientists believed that whale sharks largely navigated the world through their sense of smell, but these two distinct evolutionary defenses could mean that vision is much more important to the species than previously thought.

In Switzerland, It Is Illegal to Own Just One Guinea Pig

The Swiss are known for their historic commitment to neutrality, but they’ve also taken a firm stand on one of the most important issues of our time: guinea pigs. Because guinea pigs are social creatures who grow lonesome without a friend, it’s illegal to own just one of them in Switzerland. The law was introduced in 2008 as part of a legislative effort to grant social rights to pets. Should one guinea pig depart this mortal coil and leave its companion alone — and its owner in potential legal trouble — rent-a-guinea-pig services have emerged as a temporary solution.

Guinea pigs aren’t the only pets afforded special status in Switzerland. Goldfish are also prohibited from being kept alone, cats must at least have access to a window where they can see their fellow felines prowling around, and, for a time, dog owners were required to take an obligatory training course with their pooch (although that law was repealed in 2016).

Some Animals Can Pause Their Pregnancies

Evolution has devised a mind-boggling number of amazing methods for perpetuating life on Earth. But one of nature’s most impressive tricks is pumping the brakes on pregnancy with a process known as embryonic diapause. This isn’t a rare prenatal feat, either: An estimated 130 mammal species, such as mice and seals, can pause a pregnancy for anywhere from a few days to as many as 11 months, as is the case with the tammar wallaby (Notamacropus eugenii). The pause usually occurs during the blastocyst stage, when an embryo forms in the uterus but doesn’t embed into the uterine wall until conditions are right.

Scientists have identified two reasons why some mammals pause pregnancies. When animals are nursing, a rise in hormones prevents embryos from implanting, which gives the nursing young time to wean off their mother. The second reason is a bit more complicated, but certain animals can pause pregnancies when external conditions — such as a lack of food or harsh temperatures — are not ideal for raising a newborn. Scientists have known about this kind of diapause since at least the 1850s, but are only now beginning to understand its inner workings.

Some Dogs Can Understand 250 Words

Dogs are man’s best friend, and the canine ability to understand human words has gone a long way to solidify that world-changing relationship. According to the American Psychological Association, the average dog can understand 165 words, and “super dogs” — those in the top 20% of canine intellect — can understand around 250 words. Dog intelligence can be divided into three main types: instinctive (what the dog is bred to do), adaptive (what a dog learns from its environment), and working/obedience (what a dog is trained to do). Research into the levels of working/obedience intelligence in various dog breeds shows that border collies displayed the highest levels, followed by poodles, German shepherds, and golden retrievers. With the ability to also understand simple math (1+1 = 2, for example), these “super dogs” have an estimated cognitive ability of 2- to 2.5-year-old humans.

Elephant Trunks Have More Than 40,000 Muscles

The evolutionary philosophy of elephants might be described as “go big or go home.” Elephants are the largest land animals on Earth, sport the largest ears of any living creature, and are all-around the strongest mammals by a long shot. But their most famous feature is their trunk, which can grow to 6 feet long. The trunk is central to the elephant’s survival, helping the beasts breathe, smell, eat, and drink, and it’s controlled by a network of 40,000 muscles. By comparison, the human body has only around 650 muscles total.

The Longest Nonstop Animal Flight Was 11 Days

The animal kingdom is filled with amazing migrations. From the hordes of wildebeest stomping across the Serengeti to the lumbering blue whales along the Pacific Coast, seasonal journeys sometimes thousands of miles long can be found in just about every ecosystem on Earth. But one animal stands out among the rest of these impressive travelers: the little-known and criminally underrated bar-tailed godwit (Limosa lapponica). Preferring summers in Alaska and winters in Australia or New Zealand, these large, noisy sandpipers make an epic voyage twice a year. While it’s not the longest migration in the world overall, the bar-tailed godwit flies between its two travel destinations nonstop in a journey that can last 11 days or perhaps even longer.

On October 13, 2022, a 4-month-old bar-tailed godwit with the rather uninspiring name “B6” took flight for Australia, likely after fattening up on crustaceans and mollusks at the Yukon-Kuskokwim Delta in southwestern Alaska. Before the bird departed, the United States Geological Survey (USGS) and U.S. Fish and Wildlife Service tagged B6 with a solar-powered satellite transmitter to better understand the flight characteristics of juvenile godwits. After 11 days of nonstop flying, B6 arrived in Tasmania, Australia, on October 24, having traveled 8,425 miles. The USGS confirmed that this is the longest recorded nonstop flight of any animal on Earth, beating out a record of 8,100 miles set the year before by 4BBRW, an adult bar-tailed godwit. To put the achievement in perspective, bar-tailed godwits can fly across the entire Pacific Ocean without stopping at an age when humans are barely capable of lifting their own heads. Let them be underrated no longer.

Feature image credit: Original photo by Ian Parker/ Unsplash