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8 Bizarre Facts About Animal Reproduction

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There's no rule that regulates how animals obtain the necessary genetic material to reproduce—and as a result, there is a lot of weird animal sex going on out there.

1. BANANA SLUGS MATE USING PENISES ON THEIR HEADS.

Banana slugs are huge, they eat your garden, and they leave a slimy trail as they squirm across the ground. Their method of reproduction is no more pleasant than their appearance: The scientific name for one species of banana slug is Ariolimax dolichophallus, the second part of which means “long penis,” and it’s apt. The invertebrates' penises can be 6 to 8 inches long—the entire length of the slug's body. When it's time to get down, the penises grow out of pores in the head. It isn’t unusual for the penis of one slug to get stuck inside the other during copulation; to solve this uncomfortable situation, the slug on the receiving end will eat the penis that's stuck inside it.

2. MOUSE SPERM IS BIGGER THAN ELEPHANT SPERM.

Sorry, dudes: The size and shape of a male animal's sperm is more related to the biology and mating practices of the female—which is why mouse sperm is longer than the sperm of the biggest land animal on Earth, the elephant.

Two major factors in sperm size include the literal length and size of the female reproductive tract and how many mating partners the females have. Mice produce big sperm because, in most species, females have a lot of partners. The grouping of sperm can help to increase its competitiveness in promiscuous animals. Accordingly, the deer mouse has sperm equipped with small hooks that helps them clump together in groups of up to 35 sperm to fight their way to the egg. Grouping sperm allows the cluster to swim in a straighter line to the egg; the ideal number is seven. Too many spermatozoa will eventually start working against each other. Meanwhile, female elephants have a very long reproductive tract (more on that below), so male elephants have evolved to produce more but smaller sperm to combat the risk of dilution. To follow the reproductive strategy of mice sperm, elephant sperm would need to be scaled up enormously to make a difference. 

3. ELEPHANT PENISES ARE PREHENSILE.

Speaking of elephants: The elephant penis is so huge that males can rest on it like it’s a leg. When erect, it can weigh in at 66 pounds and can be more than 3 feet long. It’s also prehensile, which means that an elephant can move it around and even use it to scratch hard to reach places. As we mentioned, female elephants have long reproductive tracts—nearly 10 feet from start to finish—and the vagina doesn’t begin until about 4.27 feet in, so the elephant penis doesn't enter the vagina.

4. BEE SPERM WAGES WAR.

Male honey bee drones are infamous for extreme breeding. These bees have an internal penis—a.k.a. an endophallus—which, during copulation, is turned inside out and inserted into the queen. As he ejaculates, the drone falls back, breaking off his genitalia inside the queen and dying in the process. In theory, this sacrifice would lock his sperm inside and block out any competitors', ensuring that his genes were passed on. But unfortunately that's not what happens. As Social Insects: An Evolutionary Approach to Castes and Reproduction explains, “The next [drone] to copulate removes the mating sign [the endophallus plug] of his predecessor with the hairy ventral part of his own endophallus before he is able to insert its bulb and ejaculate the semen.” The next drone will do the same, and on and on. Of the 90 million sperm that end up in the queen's oviducts, only 7 million make it to a pouch called the spermatheca. She uses that sperm over the course of her life to fertilize eggs.

That is just the start of the story when it comes to bee sex. In species where multiple males mate with the queen, the sperm wage war with each other inside of her. (This happens in some species of ants, too.) When males get a little too violent, queens from some species will give off chemicals to calm everyone down.

5. ONE AUSTRALIAN MARSUPIAL HAS SEX UNTIL IT DIES.

The Antechinus is a mouse-like marsupial that eats insects, nests in trees, and has so much sex that it literally dies. By the time they hit 11 months old, males of this species have produced all the sperm they'll create in their short lifetimes; for the next couple of weeks, they'll go at it for up to 14 hours at a time with one female before moving on to another, over and over again, until their bodies break down. The male's fur will fall out; he'll bleed internally; he'll get gangrene and any number of other infections, ultimately dying before he reaches one year. But he's chasing tail up until the end: As Diana Fisher from the University of Queensland told National Geographic, “By the end of the mating season, physically disintegrating males may run around frantically searching for last mating opportunities. By that time, females are, not surprisingly, avoiding them.” The ladies are a little luckier, at least if they're of larger Antechinus species: Between 30 and 50 percent of them will live to produce two litters.

6. NAKED MOLE RATS HAVE DEFORMED SPERM.

The wrinkly, nearly blind naked mole rat is a successful breeder despite how inept its sperm is at being sperm. Small, malformed—many have multiple heads or are shaped oddly—and deficient in the mitochondria that most mammal sperm rely on for energy, just 15 percent, max, of the naked mole rat's sperm can swim; only 1 percent can move quickly. The animals don't produce that much sperm, either. These weird quirks may be due to the fact that the queen mates with only one male, so speedy, normal sperm isn’t necessary to guarantee the continuation of the species.

7. FEMALE NEOTROGLA PENETRATE THE MALES.

Neotrogla, a fly-like insect that lives in a cave in Brazil, is the first-ever species found that has “opposite” genitalia. The females are equipped with spiny, penis-like genitalia called gynosomes, which they use to penetrate the male; then, the insects get it on for up to 70 hours as the male transfers sperm and nutrients to the female. If the two are separated during copulation, the male’s insides will be ripped out while the female remains intact.

8. MONOGAMY MAKES FOR SMALL GORILLA PENISES.

You'd never know it by looking at them, but male gorillas have surprisingly tiny penises: They measure just 1.5 inches in length when erect. How can an animal that weighs up to 485 pounds be so humbly endowed? It's because primate mating practices are a huge factor in the evolution of the males' genitalia. When males have to compete among other males—as the sexually promiscuous bonobos do—the species' penis size is bigger. In gorilla society, male silverbacks mate with many females who are all monogamous to him. No reproductive competition equals a tiny penis. 

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These Sparrows Have Been Singing the Same Songs for 1500 Years
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Swamp sparrows are creatures of habit—so much so that they’ve been chirping out the same few tunes for more than 1500 years, Science magazine reports.

These findings, published in the journal Nature Communications, resulted from an analysis of the songs of 615 adult male swamp sparrows found in six different areas of the northeastern U.S. Researchers learned that young swamp sparrows pick up these songs from the adults around them and are able to mimic the notes with astounding accuracy.

Here’s what one of their songs sounds like:

“We were able to show that swamp sparrows very rarely make mistakes when they learn their songs, and they don't just learn songs at random; they pick up commoner songs rather than rarer songs,” Robert Lachlan, a biologist at London’s Queen Mary University and the study’s lead author, tells National Geographic.

Put differently, the birds don’t mimic every song their elders crank out. Instead, they memorize the ones they hear most often, and scientists say this form of “conformist bias” was previously thought to be a uniquely human behavior.

Using acoustic analysis software, researchers broke down each individual note of the sparrows’ songs—160 different syllables in total—and discovered that only 2 percent of sparrows deviated from the norm. They then used a statistical method to determine how the songs would have evolved over time. With recordings from 2009 and the 1970s, they were able to estimate that the oldest swamp sparrow songs date back 1537 years on average.

The swamp sparrow’s dedication to accuracy sets the species apart from other songbirds, according to researchers. “Among songbirds, it is clear that some species of birds learn precisely, such as swamp sparrows, while others rarely learn all parts of a demonstrator’s song precisely,” they write.

According to the Audubon Guide to North American Birds, swamp sparrows are similar to other sparrows, like the Lincoln’s sparrow, song sparrow, and chipping sparrow. They’re frequently found in marshes throughout the Northeast and Midwest, as well as much of Canada. They’re known for their piercing call notes and may respond to birders who make loud squeaking sounds in their habitat.

[h/t Science magazine]

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16 Playful Facts About Otters
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These adorable aquatic mammals are clever, chatty, and oddly aromatic.

1. THERE ARE 13 SPECIES OF OTTERS, AND JUST ABOUT ALL OF THEM ARE DECREASING.

Only one otter species seems to be thriving, and that's the North American River Otter. The other 12 otter species were recently identified by the International Union for Conservation of Nature (IUCN) as having decreasing populations, and five otter species are already on the endangered list. Among the endangered are the sea otters along the California coast, which are threatened by "environmental pollutants and disease agents." Others, like the marine otters of South America, have had their numbers reduced because of poaching, as well as environmental concerns.

2. ZOROASTRIANS THOUGHT THE OTTERS TO BE NEARLY SACRED CREATURES.

This ancient monotheistic religion considered otters to be the dogs of the river or sea and had strict rules forbidding the killing of otters. It was thought that otters helped keep water purified by eating already dead creatures that might contaminate the water source if they were allowed rot. They would also hold ceremonies for otters found dead in the wild.

3. OTTERS HAVE VERY DISTINCTIVE POOP, AND THAT SCAT HAS ITS OWN NAME.

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Otters use their dung—known as spraint—to mark territory and communicate with other otters. The mammals like to keep things organized within their communities and will designate certain areas to be used as latrines. Spraint scents can vary, but often are (relatively) pleasant—one expert described them as not "dissimilar to jasmine tea." Spraint composition is unique to each otter, and the creatures can identify each other by the smells. Scientists suspect otters may even be able to determine the sex, age, and reproductive status of the spraint dropper just from a quick whiff. And since otters have superb metabolisms and must eat up to 15 percent of their body weight each day, there's a lot of spraint to go around.

4. OTTER MOMS ARE TOTALLY GAME FOR ADOPTION.

In 2001, a female otter at the Monterey Bay Aquarium gave birth to a stillborn pup on the same day a stranded pup was discovered in the wild nearby. The aquarium staff had previously tried raising pups themselves but found that hand-raised otters became too attached to humans to be released back into the wild. So instead, they dropped the pup in with the female otter, and she immediately went into mom mode. The aquarium has since devised a system of hand-rearing pups for the first 6-8 weeks—mostly for bottle feeding purposes—before handing the pups off to female otters for raising. At six months, the pups are released back into the wild with generally strong results.

5. THEY HAVE THE THICKEST FUR OF ANY MAMMAL IN THE ANIMAL KINGDOM.

Otters can have up to one million hairs per square inch. There are two layers of fur—an undercoat and then longer hairs that we can see. The layers manage to trap air next to the otter's skin, which keeps the otters dry and warm and also helps with buoyancy. Otter pups have so much air trapped in there, they actually can’t dive under water, even if they want to.

6. AN OTTER IS SOMETIMES ONLY AS GOOD AS HIS TOOLS.

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Otters love to eat shelled animals, like clams, but they aren't equipped with the strength to open their food without some help. Therefore, they are big on tools and will often use rocks to help crack into dinner. While they hunt for food underwater, they’ll often store a rock in the skin under their arms for later use.

7. OTTERS ARE POPULAR IN NATIVE AMERICAN CULTURE, BUT FOR VARYING REASONS.

Some tribes consider the otter to be a lucky animal and a symbol of "loyalty and honesty." But some, particularly in present-day Canada and Alaska, viewed the river otter "with awe and dread" and associated the creatures with the undead and drowning. They forbid eating the creatures and were offended when colonial Europeans began hunting the river otters and selling their furs.

8. GIANT OTTERS ARE SUPER CHATTY.

In 2014, a study of giant otters found that the river-dwellers have 22 distinct noises they make for different situations. On top of that, pups have 11 of their own calls that they intersperse with "infant babbling." Among the most notable calls: a "hum graduation" used to tell otters to change directions and a "Hah!" shout when a threat is nearby.

9. OTTERS AND HUMANS CAN COLLABORATE.

In Bangladesh, otters help fisherman maximize their haul. For centuries, fisherman have been training otters to act as herders and chase large schools of fish into the nets.

10. DRONES MAY HELP SCIENTISTS BETTER STUDY OTTERS IN THE WILD.

Keeping an eye on otters in the wild is a tricky task. In the past, observers have usually set up telescopes on shore to try and monitor otters at sea while on land. Otters won't act naturally with humans nearby, and using a telescope on a boat can get tricky in the rollicking ocean. But now, scientists are using unmanned drones with cameras to get an aerial look at otters in their element, making it easier to monitor the creatures as they dive for food and go about their day.

11. SEE A GROUP OF OTTERS? THAT'S A ROMP. OR A BEVY.

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Or a family or a raft. Otter groups go by a few different monikers, all of which are fairly unique to that crew. Generally, a group of otters on land will go by a romp, while a group hanging in the water is called a raft.

12. OTTERS ARE BIG ON PLAY TIME, AND MAKING SLIDES IS AMONG THEIR FAVORITE GAMES.

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Otter families are usually limited to pups and their mothers, and that duo will spend most of their time either feeding or sleeping. In the downtime, though, otters love to play and will often build themselves slides along the banks of rivers.

13. CALIFORNIA SEA OTTERS DIVIDE THEMSELVES IN DIET GUILDS.

Once thought to be gone from the area completely, southern sea otters—known as California sea otters—have been making a comeback in recent years. But with their numbers hovering around just a few thousand, researchers have kept a close eye on the population and their studies have revealed an interesting social structure. The otters, which need to consume 25 percent to 35 percent of their body weight every day in order to maintain their blubber stores and keep themselves warm in the cool waters, are divided into three "dietary guilds": Deep-diving otters that dine on abalone, urchins, and Dungeness crab; medium divers who subsist on clams, worms, and smaller shellfish; and those that stay in shallower waters, feeding on black snails.

14. THE FIRST EUROPEAN TO SET FOOT IN ALASKA WAS ALSO THE FIRST TO DESCRIBE SEA OTTERS.

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Georg Wilhelm Steller was the first to scientifically describe numerous new animals on the 1741 explorative voyage from Russia. Aboard the St. Peter, Steller and other 18th-century explorers crash-landed on mainland Alaska after getting separated from its sister ship. Steller was the first European to set foot on the icy land. Over the course of a rough Alaskan winter, he meticulously documented many species, and while some have since gone extinct (like a sea-cow he described that was hunted into extinction), the adorable otter was among his initial discoveries.

15. BABY OTTERS ARE BUOYANT, BUT THEY CAN'T SWIM ON THEIR OWN.

A mother will often wrap the babies in kelp to keep them in one place while she hunts. Or, she might rely on human resources and otter ingenuity to find a makeshift “playpen” for her pup.

16. THEIR BEHAVIOR ISN'T ALWAYS ADORABLE.

Like many animals, otters sometimes behave in ways that aren't exactly within the bounds of what humans would consider morally acceptable. Even if you find them otherwise adorable, otters' mating habits will no doubt make your stomach turn.

Male otters' mating techniques are violent. They bite their female partner's face during copulation to keep her from slipping away, leaving her with substantial facial wounds. It's not uncommon for female otters to die as a result of these aggressive encounters, either through drowning or from their wounds becoming infected. Male otters have also been known to violently copulate with other species—most notably, baby seals [PDF]. The behavior doesn't stop when the seals die from the trauma. Otters have been known to guard and have sex with the bodies of their victims for up to seven days after they've died.

Scientists hypothesize that these seemingly counterproductive mating habits might be the result of a population imbalance. In California's Monterey Bay, where scientists observed otters trying to copulate with the week-old bodies of dead baby seals, there are far more male otters than females. Facing a lack of female partners, male otters may be engaging in what researchers call "misdirected sexual activity." The area in the bay where the scientists observed the most otter-on-seal mating sessions was also where there was a high population of transient male otters, ones that, unlike more dominant males, don't have an established territory filled with potential mates. In the absence of females of their own kind, then, they turned their typical sexual responses toward the seals. Nature, unfortunately, isn't always pretty.

A version of this story originally ran in 2015.

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