Scientists say they are seeing more seals trying to mate with penguins, but can't understand why.

Seals are forcing penguins into sex and occasionally killing them once they get their sexual release.



That was the observation scientists made on Marion Island in the sub-Antarctic, with their findings and rather disturbing videos published in the online edition of the journal Polar Biology, BBC reported.

They first discovered a fur seal attempting to copulate with a king penguin in 2006 and returned this year to see if it was still happening.

It was.

They observed on four separate occasions young male seals sexually coercing what appeared to be healthy penguins of unknown gender.

The seals chased, captured and mounted them.

The seal then attempted copulation several times, lasting about five minutes each, with periods of rest in between.

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.

The scientists speculated the sex act at the time may have been the behaviour of a frustrated, sexually inexperienced seal. Or an aggressive, predatory act. Or a playful one that turned sexual.

Although it was not a complete shock, the scientists still said the findings were surprising and it could be getting worse.

"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," Nico de Bruyn, of the Mammal Research Institute at the University of Pretoria, told BBC.

"I genuinely think the behaviour is increasing in frequency."

The incidents were 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.

De Bruyn said seals had the capacity to learn, so the increase in cases could be attributed to male seals seeing each other coercing penguins, then attempting it themselves.

Like most birds, penguins do not have external genitalia and instead possess an opening called a cloaca.

They mate by pressing these organs together in what was known as a "cloacal kiss", in which the sperm was transferred to the female.

Traumatically for the penguins, some of the seals were thought to have successfully penetrated the victims' cloacas during the act as blood was observed around the area afterwards.