Mythconception - do most birds really mate for life?

03 July 2018

Interview with

Georgia Mills

Birds have a reputation for being the most lovey-dovey animals, after all - most of them mate for life! Don't they? Georgia Mills has ruined the romance for all of us...

Georgia - However confusing, dramatic, or upsetting human relationships can be we can all take solace from that beautiful image of all the different species of lovebirds who stay true to each other forever and bond for life. Or do they?

Birds are unusual in that most of them do just have one partner. The most common pattern of mating in animals is called “polygyny,” and this is where one male has a relationship with two or more females. But many species of birds have a one on one relationship and we call this “monogamy.”

In fact, 90 percent of bird species are monogamous but this doesn’t always mean ‘till death do us part.’ Often this will just mean a pair will stay together for one breeding season to bring up their chicks before looking for a new partner. But there are some species like swans, geese, and cranes who do stay together for life. But are they true to each other? This is a bit more of a grey area. Because, you see, advances in genetics have shattered our illusions of feathered fidelity. Those birds have been playing away from the nests.

When scientists actually do genetic testing on a nest around 30 percent of the eggs in most species will not be related to the male lovebird. Those blue tits, herons and, unsurprisingly, shags have been out philandering while their partner isn’t looking.

And the ultimate adulterers are the superb fairy wrens. While they present the image of perfect familial devotion, 65 percent of their chicks will be from a different daddy. And this is because the females sneak off just before dawn to the territories of the sexiest males and then, well, ‘the early bird catches the sperm.’ And what female fairy wren could resist those bright blue males seductively dancing and presenting them with yellow flower petals.

All this debauchery shocked people when it first came to light, but there’s a good evolutionary reason for it. Females can only have so many eggs, so it’s a good idea to increase the genetic diversity of their broods so that at least some of them will survive. And, if you’re a male bird, it’s generally a good idea to have as many chicks as possible. And even so, there are still a small minority of bird species that, as far as we know, do mate with each other exclusively.

There are some other animals that do only mate with one partner their entire life but usually the reasons are less than romantic. Some very short-lived species simply don’t have the time, and for others mating is the last thing they ever do. Some species of male spider throw themselves into their special one’s jaws and get busy being eaten alive while they finish their romantic encounter. And, rather grotesquely, some species of reptiles, bees, and primates try and ensure their partner won’t mate with anyone else by gluing up the reproductive tract - it’s what's called a “mating plug.”

So, in summary, if you’re looking for inspiration on romantic relationships... don’t look too closely at the animal kingdom.


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