A group of researchers say they have observed three new incidents of fur seals trying to have sex with king penguins on an island located in the sub-Antarctic Indian Ocean.

*WARNING: Readers may find details of this story disturbing.*

In a study published last week in the journal Polar Biology, researchers from the University of Pretoria said they have observed three different occurrences of Antarctic fur seals sexually coercing king penguins on Marion Island.

The researchers captured the three incidents on video. Dr. P.J. Nico De Bruyn, one of the study's main authors, had previously observed a similar case in 2006.

*WARNING: Viewers may find this graphic video disturbing to watch.*

According to the study, all four incidents followed a similar pattern, where a male fur seal chased, captured and then mounted a king penguin.

"The seal then attempts copulation several times with periods of rest in between," the study said.

In three of the four cases, the fur seals released the penguins after forcing themselves on them. But in one interaction, the seal killed the penguin after sex and then ate parts of its neck and chest.

While the hunting of king penguins has been observed on the island in the past, the researchers say these four incidents may be part of an "emerging" sexual behaviour among the seals.

The researchers hypothesize that two drivers may be prompting the "unusual behaviour."

The first hypothesis is that it may be an extreme case of reproductive interference (interspecies sex), caused by a lack of available female seals.

The authors say the seals may be specifically engaging in "heterospecific mating attempts," which involve attempts to mate without any preceding courtship.

"With the continued growth of the (fur seal) population at Marion Island, the population might be reaching levels where there exists increasing competition for access to females," the researchers say.

The second hypothesis is that the fur seals may be learning the behaviour from each other and may be associating it with some sort of reward.

The authors note that past research has shown that seals have demonstrated an ability to learn.

"The group is considered highly adaptable to novel circumstances and display behavioural plasticity when faced with environmental pressures," they write.

"Learning behaviour is usually associated with a reward or threat – what would the value of this learned behaviour be to the seal?"