Monogamy in the Animal Kingdom

Valentine’s Day is here, which means love is in the air. But as Rowena Tylden-Pattenson explains, we aren't the only ones who like to share it with that special someone (or something).

Rowena Tylden-Pattenson
12th February 2018
Never come between a swan and its mate.

There’s always a section in Valentine’s Day cards that is dedicated to cute animals; picture two swans with their necks wrapped in a heart and you'll know exactly what I mean. Swans are almost the epitome of monogamy in animals; an elegant bird that mates for life, the males one of the few species to help incubate eggs. In more recent years, science has discovered this monogamy is not just heterosexual in swans either; studies have shown that 20% of all swans are in a homosexual relationship. The only reason these paired males may mate with a female is to later steal her eggs to raise with their male mate after driving her away from the clutch. Male swan pairs have also been known to adopt abandoned clutches – very romantic, really (well not the stealing eggs bit).

But monogamy in animals is not just distinct to swans; there are plenty of other animals that also present this trait. Around 90% of birds are socially monogamous, including barn owls, bald eagles and macaroni penguins. What could be more romantic than the mating displays of these birds; barn owls are brought gifts of dead mice by males to be rewarded with the sexual croaking of females, while macaroni penguins cackle and swing their heads from side to side in something called an ‘ecstatic display’. I’d definitely be happy with a dead mouse as a valentine’s day present (it’s probably more than what I’m getting currently!). But then again, I’m also an ecologist.

A bird completely against the thought of monogamy is the humble dunnock. A small, drab British garden bird, dunnocks are easily overlooked. Perhaps that’s why they so happily partake in polygymy or polyandry, with male birds gathering flocks of females to mate with – or females sharing multiple males, depending on food resources available. They can also mate in a 10th of a second! But that doesn’t mean a female is committed to a particular male; females can ‘eject’ sperm from their cloaca; rival males actively encourage this by pecking at the female. Apparently these dull birds are quite the sexual deviants.

Many animals are no strangers to homosexual monogamy either, with around 1,500 species exhibiting this characteristic. Ninety per cent of sexual activity undertaken by giraffes is homosexual, including foreplay of up to an hour called ‘necking’, where animals rub their long necks against one another (and no, that’s not a euphemism). Female Layson’s Albatross, far-flying seabirds, have chicks fathered by males in another committed relationship, to then be raised by two females in a relationship. And many bottlenose dolphins are bisexual. Who knew?

Giraffes love a good neck on. Photo: Luca Galuzzi (Lucag) [CC BY-SA 2.5] via Wikimedia Commons

Not all monogamous animals are quite as charismatic however. Under the sea, French angelfish make aggressive pairs, defending their territories. Potbellied seahorses have reversed roles in the breeding process, with males carrying the young through to birth. Females compete for their attention, with males selecting their mates. Some mate-switching occurs in other species of seahorse, but generally they seem to stay together for some period of time.

But seahorses are still fairly attractive creatures to have on a greetings card. Well, let me present to you the Schistosoma mansoni flatworm. These parasitic flatworms use freshwater snails and humans as hosts. The flatworm penetrates through a human’s skin, normally at a hair follicle, with larvae moving into the lungs to feed on the blood there. Once fully matured, adults move towards the heart, forming pair bonds there and producing up to three hundred eggs a day. If that’s not romance, I don’t know what is.

Only around 3% of mammals are monogamous

Too grossed out? Another fluffy one for you, then. Grey wolves normally find their life partner by the time they hit two, staying with their partners for life and producing a litter of pups every year. Equally sweet, beavers co-parent kits (that’s what baby beavers are called). In a beaver social unit, other adult beavers also take care of young beavers, in one big happy beaver family.

But although there are all these weird and wonderful animals that are monogamous, only 3% of mammals are monogamous. I think that’s still enough to mix up the monogamy of greeting cards and their relationship with swans. Or maybe it’s just me that wants a card this year with a flatworm on it?

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