Fur Seal Sex With Penguin: Why Does It Happen?

At first it was thought that sex between animals of different species was a case of mistaken identity, but new research suggests otherwise.

Antarctic fur seal males have been seen forcing themselves on king penguins multiple times in shocking sexual acts that are radically changing the way animal experts attempt to explain such seemingly bizarre behavior.

At first it was thought that sex between animals of different species was a colossal error -- a result, maybe, of mistaken identity. The occurrences of male seals raping penguins, documented in the latest issue of the journal Polar Biology, suggest otherwise. Instead it may be a learned behavior by hormone-fueled males, which could weaken the overall reproductive fitness of both animals if it gets out of hand.

The seal-penguin rapes "may be learned behavior associated with some sort of reward, or it may be an extreme case of reproductive interference," wrote senior author Nico de Bruyn of the University of Pretoria and his team in the journal.

"Reproductive interference occurs when individuals of one species engage in reproductive activities with individuals of another species, and when these interactions reduce the fitness of one or both species," Emily Burdfield-Steel, who is a researcher at the University of Jyväskylä in Finland, explained to Discovery News.

The fitness of the birds is definitely reduced, since at least one penguin victim was seen bleeding between its legs. The seal population would also appear to suffer, given that mating requires time and energy that, in this case, would not result in offspring.

The possible reward, however, could be the male's immediate sexual fulfillment.

As de Bruyn and his team wrote of one seal-penguin encounter: "The seal ran up to the penguin and bumped it down. It lay on top of the penguin and started thrusting its hips in a copulatory fashion. The seal's erect penis was clearly visible."

A disturbing video (warning: it's graphic) that has since gone viral shows one of four such encounters that the researchers observed on Marion Island, located in the Indian Ocean just north of Antarctica.

De Bruyn first saw an Antarctic fur seal attempt to copulate with a king penguin six years ago on the same island. Although this location has been heavily studied for three and a half decades, the behavior had never been noted before. Recently, on a return visit, de Bruyn and his team documented the four seal-penguin rapes, so they think the behavior is "newly emerging."

The region has a "bachelors beach" dominated by young male seals, so without many female seals around, the male seals could wind up chasing, for sex, what is normally a dinner item for them: penguins.

The seal-penguin copulations all happened during the seal's breeding season on the island, from late November to early January. On one occasion, a male seal ate a penguin that it had just raped.

In terms of why a predator would suddenly view a prey animal sexually, Burdfield-Steel suggests that raging hormones could reduce an individual's choosiness.

"For the less choosy sex," she said, "this keenness to mate may lead to individuals being less discriminating when choosing mates and therefore more likely to fail to differentiate between species."

She and colleague David Shuker report that there are at least 167 documented instances of animals having, or attempting to have, sex with other species. This excludes hybridization, where such mating can lead to offspring (think mule). Humans, of course, are included in this group -- everything from the Bible to cave art has shown that some people have practiced bestiality.

In other examples, male sea otters have been documented raping and drowning young seals. Another viral video shows a young chimp raping a frog. Yet another video shows a rabbit attempting to mount a dog. Most dog owners have stories of their pets going at it with a person's leg, arm or other reachable area.

It remains to be seen what will happen next on Marion Island but, for now, the sex between different species appears to be relatively rare, which is usually the case throughout the animal kingdom.

As animal researcher Ana Amaral of the University of Lisbon told Discovery News, "In most cases found in nature, each species favors its own kind when mating."

Not all mixed species sexual encounters are violent and unproductive. Some pollinating insects regularly attempt to mate with flowers. For example, male orchid dupe wasps find Australian tongue orchids so alluring that they will linger on the orchid's petals, leaving behind blobs of ejaculate.

An Antarctic fur seal seen among king penguins.

Adelie Penguins

Frozen Planet began airing on Discovery Channel on March 18. In this ultimate portrait of animals in the frozen zones of the Arctic and the Antarctic, we get to see, up close, the animals that live in this habitat like we have never seen them before. The stars of the show are the animals, like the Adelie penguins in Cape Crozier, Antarctica (seen here). The following is a look at some of our favorite images from the series, which you can see every Sunday at 8 e/p from March 18 until April 15.

FROZEN PLANET VIDEOS: On the Discovery Channel

Great Grey 'Ghost' Owl

One of the largest owls in the world with a wingspan of between four and five feet, it is often referred to as the Great Grey Ghost or Phantom of the North because it is so reclusive.

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Unlike dark-eyed nocturnal owls, the Great Grey Owl has distinctive piercing eyes, which may be an adaptation to hunting by day.

Emperor Penguin, Ross Sea, Antarctica

During the winter months in Antarctica, male emperor penguins keeps their eggs warm. They remain alone for the six months of winter without feeding, waiting for the return of the sun and their female partners, who have been gone, feeding.

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During the depths of winter, they have to endure temperatures of minus 60 degrees Centigrade.

Sea Lion and Gentoo Penguin

A sea lion chases a Gentoo penguin onto land - both are like fish out of water and the sea lion struggles to make a kill.

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The fully-grown Gentoo penguin has no natural predators living on land, though birds will occasionally steal eggs from their nests.

Grey Wolf, Ellesmere Island, Canada

Young pups born into the High Arctic packs have a precarious life ahead of them if they are to grow to a size big enough to survive the next winter.

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Snowy Owl, Artic

Each snowy owl chick eats two lemmings a day, so the parents are kept very busy. During nesting season, predators abound as the owls are stuck on the ground to tend the eggs. Both the male and female dive-bomb predators until the chicks are able to fly and they can all escape the ground.

Beluga Whale

A beluga whale enjoys a body scrub. It uses the gravel on the beach as a loofah to scrape off old skin as it molts.

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Polar Bears, Hudson Bay, Canada

Frozen Planet captured a surprisingly playful and sociable side of polar bears.

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In the 1970s there were an estimated 5,000 to 25,000 polar bears in the Arctic. Since conservation began 46 years ago, the current population is estimated to be 20,000 to 25,000.

Musk Ox, Canadian Arctic

Musk ox are Arctic residents and are uniquely adapted to withstand the ferocious Arctic winters with a double layer of fur.

Arctic Wolf Chasing Buffalo

An Arctic wolf chases after a herd of wood buffalo, Wood Buffalo National Park, Canada.

Polar Bear Cubs

A pair of two-day old polar bear cubs. At this age they weigh less than a kilo so by weight are less than 280 times smaller than their mother.

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Over the next 12 to 18 weeks, the bears will nurse. After three or four months, they will leave the den where they were born to learn survival and hunting skills from their mother.

Grey Wolf Watches Crew

The crew filming "Frozen Planet" at Karrak Lake, Barrenlands, Canadian Arctic, encountered some incredible things. As the midnight sun glows on the horizon, a lone Arctic wolf spots the crew and eyes them curiously. After spotting them on the horizon, this wolf traveled over 6 miles to see humans, a species it was unlikely to have encountered before. "Completely naive and unafraid, he sniffed around our feet as our hearts pounded. He then gave us this quizzical last look and headed back across the horizon," crewmembers said.

Least Weasel, Finland

The least weasel is the smallest carnivore in the world; the very smallest are found in the High Arctic (weighing an ounce, average body length of about 5 inches). They stay active throughout the winter despite extreme temperatures that can drop below minus 50 degrees Centigrade. These tiny mammals are voracious hunters, tracking down voles, mice and shrews that live in icy corridors below the snow. Their slim-line bodies allow them to hunt in tunnels the same width as their prey. The snow acts as an insulator, keeping the "subnivean" world at an almost constant minus one degree, so despite their tiny bodies, these little mammals, both predator and prey, can live comfortably even in the coldest months.

Dolgan Hunter With Reindeer

A member of the Dolgan tribe rounds up his reindeer. The Dolgan live in the most northerly mainland region of the Arctic, the Taimyr Peninsula in Siberia. Siberia is also the coldest region of the Arctic, where temperatures often reach minus 60 degrees Centigrade. The lasso was first invented in Central Asia and came north centuries ago with the Dolgan's ancestors. The best lassooes are made from walrus or bearded sealskin, which the Dolgan traditionally obtain in the summer, when they bring their herds to the coast and trade with the coastal hunters.