There’s a fascinating article getting some press this week, all about a growing incidence of an extraordinary bit of animal behaviour in the islands just above the Antarctic circle. In an article in the journal Polar Biology, reported on nicely by the BBC (with more disturbing pictures and video), scientists from the Mammal Research Institute in South Africa report multiple instances of male Antarctic fur seals sexually harassing and even raping king penguins.
The image of a seal (those goofy ball-on-the-nose guys!) mounting a penguin (those dapper black and white gents with the endearing waddle) is so absurd as to be ostensibly hilarious, until you really think about what’s happening here, and then it’s not funny at all, just disturbing and fascinating. To start with, an adult fur seal is much larger and heavier than a king penguin and there’s a good likelihood that breathing of the penguin could be compromised from the weight of their attacker. But it gets worse because, like other pinnipeds, fur seals have a baculum or penis bone, which increases the degree of trauma that might result from a successful penetration. The gender of the hapless victim penguin (which was unknown for the reported cases and is hard to tell externally), would not really matter either because both male and female penguins have a cloaca or common opening that serves for solid and liquid waste disposal and also as the sexual portal of entry for normal carnal relations. I don’t know much about penguin intelligence or cognitive ability, but we should at least consider the possibility that this is psychologically traumatic for the penguin. Perhaps the ultimate moment of pause, though, comes when you read the researcher’s observation that in one of the instances, when the fur seal was finished raping the penguin, he killed it and ate it. That’s just brutal.
Why is this happening? The behaviour seems confined to sub-adult male fur seals and the researchers speculate that it may result from sexual frustration. Why then would a fur seal have blue balls? Probably because the dominant adult male in the colony is preventing them from mating with his harem of ten or more females. Fur seals are one of those pinniped species that has a “beach master” like this, so the social structure of a seal colony may predispose sub-adult males to this sort of behaviour. That’s consistent with other cases of (to use a heteronormative phrase) aberrant sexual behaviour in marine mammals, such as long term homosexual pairing in adult dolphins, blowhole sex and inter-species sexual aggression and rape between dolphin species. As one marine mammal biologist I spoke to put it, it appears that opportunities for apparently aberrant behaviours increase with increasing social complexity of the offending species. In this case, the penguins are in the wrong place at the wrong time and of the wrong approximate size and end up bearing the brunt of frustrated sub-adult seals. What makes this case so extraordinary is the giant taxonomic gulf between the two species; it’s one thing for a bottlenose dolphin to rape a spotted dolphin, but it’s another thing altogether for a mammal to rape a bird. It’s probably only possible because this particular bird is flightless and not all that formidable an opponent while on land.
One of the more interesting aspects of this behaviour is its potential role in the ecology of infectious disease (forgive me, but I come from an animal health background and when you’ve got a hammer, everything looks like a nail!). In one published example, bottlenose dolphins have problems with malignant oral and genital cancers that are caused by a papilloma virus and are sexually transmitted by the oral-genital contact that is common in the mating system of dolphins. When I look at the images of the seal raping the penguin, I see extraordinary behaviour, but I also see the raw material for the evolution of “host switching”, the process whereby pathogens and parasites can effect a jump from one host species to another. In this case it’s not a jump between species, but potentially between classes of vertebrates, and those opportunities may not come along all that often. So, beyond the immediate morbidity (and in one observed case, mortality) of this behaviour, it will be interesting to see if any long term changes to the health status of penguins (or fur seals, for that matter) in this population occur in the future. In the meantime it remains one of the more extraordinary bits of marine animal behaviour I have ever seen described.
William A. Haddad, Ryan R. Reisinger, Tristan Scott, Marthán N. Bester, P. J. Nico de Bruyn (2014) Multiple occurrences of king penguin (Aptenodytes patagonicus) sexual harassment by Antarctic fur seals (Arctocephalus gazella). Polar Biology. 10.1007/s00300-014-1618-3