The truth behind love in the animal kingdom
With spring just around the corner changes in temperature, day length and even rainfall all work together to stimulate the small pituitary gland embedded deep in the brain which, in turn, informs the body to start producing eggs or sperm, or even sometimes both. Yes, it’s Valentine’s Day and the whole world is in love. But never ask a biologist about the ‘fluffier’ side of the natural world, because we relish the chance to tell you the truth behind what you see on those wondrous nature documentaries. Nowhere is this more apt than in the case of love in nature. If you are of a sentimental disposition and love the idea of love, then please, stop reading here. For the natural world is a veritable boiling pot of orgies, cheating and divorce.
Anyone who has ever been to a local park with a pond in the springtime will have realised two things very quickly; that ducks are all perverts and that monogamy might not be as prevalent as we might think. The idea of having that ‘significant other’ is appealing, sweet and heart-warming, but alas is definitely not rooted in evidence. In fact, true examples of monogamy are very few and far between in the natural world. Even those examples which we know for a fact mate for life might need a closer examination.
Let’s get the mammals out of the way first. The vast majority are not in the habit of settling down with the love of their life. Rats, mice, weasels and stoats for example are all polygamous, which basically means that either or both parties involved have (to put it mildly) roving eyes. Badgers are largely monogamous, well, the males are at least, and although foxes are widely known to be faithful to one another, one particular study showed surprisingly high levels of polygyny (one male with multiple female partners), litters with mixed paternity and even incest. In reality, of the roughly 5,000 or so species of mammals, only around three per cent form lifelong pair bonds. Of this limited group who can claim the moral high ground are beavers, otters, some bats and a few hoofed animals.
Maybe we should look to the birds to find examples of true love. Staring out of the window into the garden and let your eyes settle on the first bird you see. Which species is it and is it monogamous? Great tit? Nope, thirty per cent are unfaithful. Blue tit? Forty per cent. A house sparrow? At least one in five nests shows cheating. In starlings, it’s one in three and the seemingly shy and retiring coal tit shows a whopping incidence of seventy five per cent in terms of nests where evidence of an ‘extra pair coupling’ is evident. Across the song birds, true (genetic) monogamy is only seen in about fifteen per cent of species. So, the garden isn’t the best place to look, maybe.
In the same way that the immortal line “But we were on a break” caused so many problems, there is a problem with semantics in the area of monogamy across the animal kingdom. While ninety per cent of all birds are socially monogamous, they are not sexually or genetically monogamous. It seems sneaky and it is. In one especially revealing experiment, male blackbirds which were already paired up with females were sterilised. Bizarrely, those females still managed to lay eggs that hatched. Awkward. Surely swans, those bastions of love in the natural world, can renew our faith here? The good news is that swans really do bond for life and are fiercely dedicated to one another. The committed pair raises clutch after clutch of cygnets throughout their lifetimes, learning from failures and successes. This opportunity to learn may be one reason they stay loyal. While mute swans are committed, it is worth noting that Australian black swans (the black ones often seen in parks) do rather let the side down and around one in seven nests shows signs of something suspect, in a genetic sense. While they don’t (usually) cheat, swans do sometimes just give in and actually ‘divorce’ their partners, if they’re especially useless at raising chicks. Around four per cent of swan couplings end this way, so that they might go on to find success.
With neither birds nor mammals being especially good at restoring our faith in love, maybe we should look further afield. For many of us, one key spring time phenomenon is the sight of ponds full of frogspawn and the resonating sound of frog choirs take us back to our childhoods. We all recognise frog spawn and kind of know what's going on there but what exactly happens when frogs get it on? Are they monogamous? No, of course they’re not. They’re worse than blue tits, even. Whereas it’s accurate to describe bird shenanigans as ‘extra pair couplings’, it might be more realistic to describe frog reproduction as an aquatic orgy. It is those males who call loudest and longest that attract the ladies and on paper, it should end up with him clasping onto the larger female, wrapping his wrists around her, holding on for dear life with specialised ‘nuptial pads’ as he fertilises the two thousand or so eggs she releases from her body. However, there are often a lot of other males who also have the same thought and in reality, what should be a tender amorous amphibious moment turns into a slippery free for all where males get so excited they all bundle on top of the unfortunate couple in such a frenzy that some will grip and try to mate with rocks, pieces of wood, anything. Believe me, be wary when sticking your hand into a springtime pond.
Although finding that special someone is close to our hearts as a species, it’s a very alien concept to our wilder natural neighbours. Practicing varying iterations of infidelity does however make some evolutionary sense. It increases the genetic diversity of broods and litters, which better prepares them against diseases and changes in the environment during their lives. It might also improve the chances of survival of the young if the best possible mate is chosen and it might even benefit the cheater in more direct ways, as there is some evidence that promiscuous female birds might gain access to the territories of males with whom they dally. So, spare a thought this Valentine’s Day for your local wildlife. You might receive a special card with a pair of loved-up animals on the cover. Just don’t read too much into it.
Professor Ben Garrod is an NWT Ambassador.