By Matt Walker 
 
 BBC 
 
 Sexual coercion among animals is extremely common 
 
 An Antarctic fur seal has been observed trying to have sex with a king penguin. The South African-based scientists who witnessed the incident say it is the most unusual case of mammal mating behaviour yet known. The incident, which lasted for 45 minutes and was caught on camera, is reported in the Journal of Ethology. The bizarre event took place on a beach on Marion Island, a sub-Antarctic island that is home to both fur seals and king penguins. At first glimpse, we thought the seal was killing the penguin 
 
 Nico de Bruyn, University of Pretoria Why the seal attempted to have sex with the penguin is unclear. But the scientists who photographed the event speculate that it was the behaviour of a frustrated, sexually inexperienced young male seal. Equally, it might have been an aggressive, predatory act; or even a playful one that turned sexual. "At first glimpse, we thought the seal was killing the penguin," says Nico de Bruyn, of the Mammal Research Institute at the University of Pretoria, South Africa. Pinniped behaviour The brazenness of the seal's behaviour left those who saw it in no doubt as to what was happening. De Bruyn and a colleague were on Trypot beach at Marion Island to study elephant seals when they noticed a young, adult male Antarctic fur seal, in good condition, attempting to copulate with an adult king penguin of unknown sex. The 100kg seal first subdued the 15kg penguin by lying on it. The penguin flapped its flippers and attempted to stand and escape - but to no avail. The seal may have been frustrated in its attempts to find a partner The seal then alternated between resting on the penguin, and thrusting its pelvis, trying to insert itself, unsuccessfully. After 45 minutes the seal gave up, swam into the water and then completely ignored the bird it had just assaulted, the scientists report. Why a fur seal would indulge in such extreme sexual behaviour is unclear. Sexual coercion among animals is extremely common: males of many species often harass, coerce or force females of their own kind to mate, while animals are also known occasionally to harass sexually a member of a closely related species. Harassment is common among pinnipeds, the group of animals that includes seals, fur seals, and sea lions; and occasionally it happens between related species. Male grey seals have been known to harass and mate with female harbour seals, for example, producing hybrids. "Sexual harassment is often more commonplace in non-monogamous mating systems, and in species where males are physically much larger than the other sex and thus physically capable of coercion or harassment," says de Bruyn. But this is thought to be the first recorded example of a mammal trying to have sex with a member of another class of vertebrate, such as a bird, fish, reptile, or amphibian. 'Too young' Chinstrap penguins occasionally indulge in homosexual behaviour, and adelie penguins sometimes "prostitute" themselves to get stones for nest-building; while one in seven emperor penguins will change partners from one year to the next. But generally, king penguins lead straightforward sex lives: males and females pair up for years on end. Marion Island is the only place in the world where Antarctic fur seals are known to hunt king penguins on land, so the idea that the fur seal was trying to eat the object of its attention made sense. "But then we realised that the seal's intentions were rather more amorous." The researchers speculate that the male seal was too young to win access to female seals, and in a state of sexual excitement, looked elsewhere. But the mating season was nearly over when the incident took place, leading the scientists to also wonder whether the seal's natural predatory aggression toward the bird became redirected into sexual arousal. Equally, the incident may have arisen because the seal was "play-mating". "It was most certainly a once-off and has never previously or since been recorded anywhere in the world to our knowledge," says de Bruyn. The penguin did not appear to have been injured by the seal, the scientists report. 
 
 
 
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 Warning: You may find the videos in this story disturbing 
 
 This media cannot be played on your device. 
 
 Things are heating up in the cold climes of the sub-Antarctic. On a remote, and mostly desolate island, seals have been caught engaging in an extreme form of sexual behaviour. 
 
 Specifically, they have been trying to have sex with penguins. 
 
 More than one fur seal has been caught in the act, on more than one occasion. 
 
 And it's all been captured on film, with details being published in the journal Polar Biology. 
 
 Perhaps it is a release of sexual frustration 
 
 The sexual behaviour of the fur seals hasn't come as a complete shock to the scientists that recorded it. 
 
 In 2006, they saw, for the first time, a fur seal attempting to copulate with a king penguin, on Marion Island, a sub-Antarctic island that is home to both species. 
 
 They published details of that incident, and speculated that the sex act at the time may have been the behavior of a frustrated, sexually inexperienced seal. Or an aggressive, predatory act. Or a playful one that turned sexual. 
 
 But the new incidents, published in the study "Multiple occurrences of king penguin (Aptenodytes patagonicus) sexual harassment by Antarctic fur seals (Arctocephalus gazella)", still surprised the researchers. 
 
 "Honestly I did not expect that follow up sightings of a similar nature to that 2006 one would ever be made again, and certainly not on multiple occasions," said Nico de Bruyn, of the Mammal Research Institute at the University of Pretoria, South Africa. 
 
 Scientists routinely monitor wildlife on the island, and look out for rare and unusual behaviour. 
 
 On three separate occasions, a research team led by William A. Haddad and de Bruyn spotted young male seals sexually coercing what appeared to be healthy penguins of unknown gender. 
 
 This media cannot be played on your device. 
 
 Two incidents occurred on Goodhope Bay, and one on Funk beach. The incident in 2006 occurred on a different beach again, called Trypot. 
 
 "This really made us sit up and take notice," said de Bruyn, of the new sightings. 
 
 All four known sexual incidents followed a common pattern. Each time a seal chased, captured and mounted the penguin. The seal then attempted copulation several times, lasting about five minutes each, with periods of rest in between. 
 
 I genuinely think the behaviour is increasing in frequency 
 
 Male and female penguins mate via an opening called a cloaca, and the seals are thought to have actually penetrated the penguins in some of the acts, which were caught on film by Haddad. 
 
 In three of the four recorded incidents the seal let the penguin go. But on one of the more recent occasions, the seal killed and ate the penguin after trying to mate with it. 
 
 Fur seals often catch and eat penguins on the island. 
 
 The incidents are the only time pinnipeds, the group that includes seals, fur seals and sea-lions, have been known to have sex with an animal from a different biological class, in this case a mammal trying to have sex with a bird. 
 
 The scientists can only speculate about why the seals are behaving this way. 
 
 But the new observations suggest that having sex with penguins may be becoming a learned behaviour among seals on the island. 
 
 "Seals have capacity for learning - we know this from their foraging behaviour for example," explained de Bruyn. 
 
 So male seals may see each other coercing penguins, then attempt it themselves. 
 
 That might explain why the number of incidents appears to be increasing. "I genuinely think the behaviour is increasing in frequency." 
 
 This media cannot be played on your device. 
 
 But "if this is learned behaviour, we really can’t think of what the reward may be for these young males," he adds. "Other than perhaps learning that these birds are an easier target to practice their copulatory skills." 
 
 The seals were not yet old or large enough to defend harems of female seals, explained de Bruyn. 
 
 "Perhaps it is a release of sexual frustration, given the hormonal surges during seal breeding season. It is very unlikely to be failed mate recognition - i.e. the misidentification of the penguin as a female seal. 
 
 "All in all it's difficult to say really," he admits. 
 
 All videos credited to William A. Haddad, and courtesy of Polar Biology / Springer. 
 
 Matt Walker is BBC Earth's editor. He is @byMJWalker on Twitter. 
 
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– Scientists are documenting "sexual coercion" in the Antarctic, and it's probably not anything like what one might think: Young male Antarctic fur seals, it seems, have been documented having sex with King penguins of undetermined gender, reports the BBC, via a study in the journal Polar Biology. Scientists observed a male seal unsuccessfully attempting to mate with a penguin in 2006, but dismissed it as a one-off. But researchers says they inadvertently observed the same thing on at least three separate occasions. "Honestly I did not expect that follow-up sightings of a similar nature to that 2006 one would ever be made again, and certainly not on multiple occasions," says a study co-author. It's believed to be the first instances of pinnipeds—which include seals, fur seals, and sea lions—having sex across biological classes, as the BBC notes, "in this case a mammal trying to have sex with a bird." Some of the seals are believed to have penetrated the penguins, and one instance turned bloody, with the seal killing and eating his victim, though that's not unusual. It's not clear what's driving the behavior, though scientists speculate that it's a learned behavior; that would explain the increase in sightings. "I genuinely think the behavior is increasing in frequency," says the co-author. Other theories include the seals blowing off sexual frustration, or using the weaker birds to practice. "All in all it's difficult to say really," says the co-author. (Meanwhile, a study previously revealed that penguins are pretty sexually depraved themselves.)