In a very disturbing development, marine biologists have documented continued instances of fur seals in the Antarctic engaging in nefarious sexual behavior – specifically, the forcible sodomy of penguins. The phenomenon was first observed in 2006, and yet another study was published last week in the journal Polar Biology. These are the only known instances of pinnipeds attempting to mate outside of their species.

The original observations were at first dismissed as exceptionally misguided behavior on the part of a young seal, or a sexually frustrated one, or an instance of playful behavior turned sexual. The newest observations, however, reveal what appears to be an emerging pattern.

“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, South Africa told BBC news.

The seals, orders of magnitude larger than the penguins, don’t have much trouble pinning and mounting the penguins if they get close enough to catch them. While some observed instances didn’t appear to result in any bodily penetration, some penguins showed signs of being violated via their cloaca, an all-purpose orifice used for both reproduction and waste elimination. The seals were seen attempting to mate several times, lasting about five minutes each with breaks in between.

While three of the four penguin victims escaped otherwise unscathed, one penguin was killed an eaten by its seal assailant. Seals are penguins’ primary predatory and often capture and eat them.

Seals have demonstrated a capacity for learned behavior, and as such the scientists believe that may be what’s happening. Still, even if the seals are capable of passing on the notion of penguin rape, the scientists have no idea why they would do so. It could be that young seals have found the penguins to be easy targets for mating practice, or a low-risk release for sexual frustration. Though they’re convinced the behavior is on the rise, explanation eludes them.

“All in all it’s difficult to say really,” de Bruyn admits.