Researchers disturbed by seal-on-penguin rape

Nature is a strange and cruel place. At least that's the takeaway from recent evidence that fur seals are sexually assaulting penguins on Marion Island, a sub-Antarctic island where the two species often share the beaches.
In the latest issue of the journal Polar Biology, scientists reveal the unusual sexual act (seal on top of penguin) has been observed more than once -- several times, in fact. Researchers first witnessed the disturbing phenomenon in 2006. They've since seen it happen three more times.
"Honestly I did not expect that follow up sightings of a similar nature to that 2006 ... and certainly not on multiple occasions," Nico de Bruyn, a researcher at the Mammal Research Institute at the University of Pretoria, South Africa, told BBC News.
Upon the 2006 observation, researchers concluded the incident might be a case of sexual frustration. But the new occurrences have scientists' befuddled. It's not clear whether sexual penetration is acheived, but in each incident a similar pattern holds. A young male fur seal chases down and pins a penguin before mounting and thrusting. Each encounter lasted roughly five minutes, sometimes split up by brief moments of rest.
On three of the four occurrences, the seal has let the penguin go. But the most recent act of abuse ended with the seal killing and eating the penguin. Fur seals have been known to occasionally hunt and eat penguins.
Despite the confusion over the disturbing act, researchers say their "mate deprivation hypothesis" is still the most likely explanation. Seals hit sexual maturity at the early age of three or four. Still young, these randy seals aren't bulked up enough to bully their way to the top of the reproductive hierarchy. Occasionally, the biologists conclude, a young male's sexual frustration boils over and he takes it out on a penguin.
The response seems to be organic, not learned, as the four incidents all occurred over several years -- separated by time and space.