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Scientists have observed fur seals coercing king penguins into sex in the sub-Antarctic.

Researchers from the University of Pretoria, in findings published in Polar Biology, said they observed seals coercing penguins into sex four times. In three of the incidents the penguin was let go afterwards. In the final instance the seal killed and ate the penguin.

It's not the first time scientists have observed this form of behaviour in the sub-Antarctic, it was first documented eight years ago. Lead scientist Nico de Bruyn said of the research: "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's team believe coercing penguins into sex may have become a learned behaviour, with male seals seeing their peers doing it, and then trying it themselves. "We really can’t think of what the reward may be for these young males," de Bruyn told the BBC. "Other than perhaps learning that these birds are an easier target to practice their copulatory skills."

He added: "Perhaps it is a release of sexual frustration, given the hormonal surges during seal breeding season. It is very unlikely to be failed mate recognition - i.e. the misidentification of the penguin as a female seal."