The BBC wildlife story begins "Warning: You may find the videos in this story disturbing." The BBC is absolutely correct. Nevertheless...

Comes the story, via the academic journal Polar Biology, about a recently rising and video-recorded phenomenon in the Antarctic:

BBC was first with the story:

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.

But three recent incidents in multiple locations of "young male seals sexually coercing what appeared to be healthy penguins of unknown gender" have set the researchers scurrying:

"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... "This really made us sit up and take notice," said de Bruyn, of the new sightings.

Seals and sea lions had never before been recorded having sex with other biological classes of animals, but nonetheless, there is a rash of fur seals now catching penguins, mounting them, and attempting "copulation several times, lasting about five minutes each, with periods of rest in between." Like this:

In one incident, the seal finished, then ate his feathered victim.

Why are the seals doing this? There's no unified theory yet, although researchers speculate "it is a release of sexual frustration, given the hormonal surges during seal breeding season," or merely practice for skills they might later use in effective mating.

As for why it's happening more often, scientists think the pack is learning the deviant behavior from the first few seals who attempted it.

Still, de Bruyn told the BBC, "[I]f this is learned behaviour, we really can't think of what the reward may be for these young males."