"At first glimpse, we thought the seal was killing the penguin," Nico de Bruyn, lead author of the recent study, told the BBC in 2008. But the incident, which lasted 45 minutes, couldn't be mistaken for attempted murder in the end: Instead, the young adult male seal was attempting to mate with a penguin of unknown sex. From the BBC:
After 45 minutes the seal gave up, swam into the water and then completely ignored the bird it had just assaulted, the scientists report.
They thought that this was probably just an isolated incident, carried out as an act of aggression, confusion or misguided playfulness. "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," de Bruyn, a researcher at the Mammal Research Institute at the University of Pretoria, told the BBC.
But now they're reporting four incidents in total. Each time, a seal would chase, catch and mount a penguin, then attempt to mate with it several times. On one occasion, the assaulted penguin was killed and eaten after the incident — which on its own is a much more common interaction for the two species to have.
Interspecies mating isn't totally uncommon, with some scientists estimating that about 10 percent of animals intermingle. But the vast majority of these cases involve animals that are very similar in genetic composition and appearance, and can produce hybrid offspring with each other. Sometimes these meetings are cases of mistaken identity, but interspecies mating and hybridization can also be used as an evolutionary tool in interspecies competition for survival.
But that's not the case with seals and penguins: The penguins are clearly in distress, and it's obviously unlikely for a seal to confuse a penguin for a potential breeding partner.
It might be that male seals are learning this behavior from watching each other, the authors report. It could be that they're collectively realizing that the birds are easy targets as they look to vent the sexual frustration caused by mating season hormone spikes. It could be that females are hard to come by on these beaches, leaving young male seals looking for other outlets.
In another part of the world, seals can actually end up being on the receiving end of these kinds of assaults: In 2011, researchers reported incidents of sea otters copulating with (and killing) baby harbor seals.