It’s a shame when two humans  have to go their separate ways.

But usually, we can also see  that they’re better off for it. Divorce is just one of those  realities we have to put up with.

And yet for some reason, we’re much more romantic  when it comes to animals, especially birds. TV documentaries tell us they  “mate for life,” and we picture   them lovingly hatching chicks together  and caring for them in perpetual bliss. Which is by no means always the case.

Birds will cheat, run away, and yes, divorce. Even in species that supposedly mate for life. Here’s why some birds might find  themselves in divorce court. [♪ INTRO] First off, we should probably clarify  the language we’re using here. “Divorce” is the term used in the  literature for when these pairs split up.

Many birds will have a pair bond where a male and   female couple will raise that  season’s young with each other. That’s the classic, warm fuzzy bit we all know. The real question is whether or not  they come back together again next year.

If they do, the pair bond is going strong. If not, the pair bond is broken –  what the literature calls a divorce. But unlike humans, who split up for personal,  economic, or any number of different reasons,   birds are just responding to selective  pressures in their environment.

These birds may be the stuff of daytime  talk shows, but in this episode,   we’re not saying anything about  what humans do, or should do. Now, bird divorce is a bit of a spectrum. Some birds, like swifts and albatrosses,  have very few recorded cases of divorce.

Those are your David Attenborough happy couples. Others, like herons, simply can’t hold a  marriage together and have a 100% divorce rate. But it’s the in-between cases we’re interested   in – the ones where couples sometimes  split up, and sometimes stay together.

One 2024 study in Seychelles warblers found that   performance in reproduction was a  big reason for getting divorced. Natural selection drives all animals to pass  on their genes, so this isn’t a big surprise. Females who laid smaller clutches were a  lot more likely to get divorced than ones   laying larger ones, and this is likely because  it’s the best indicator of partner quality.

There are other things that  can ruin a breeding season,   like predators or lack of  rainfall meaning less food,   but they’re not things you can realistically  blame a partner for and are pretty unpredictable. Single studies like this one provide  us with the fine deets on the divorce,   but there are similar findings  in a lot of other studies too. A meta-analysis of divorce in birds  found that lack of breeding success is   the biggest indicator of divorce  occurring in birds as a whole,   and is generally an attempt to  improve their mating status.

Ornithologists apparently just can’t  resist the gossip of who’s dating who. In the warblers, the age of  the male also plays a big role. Older males are more likely  to be involved in divorce,   presumably as they’re getting a  bit long in the tooth… or beak.

But younger males may also split up,  due to either lack of experience in   picking a good partner, or just  breeding success on their end. For some of the fellas, it’s not  just the quality of their partner,   but the quantity of potential ones as well. One study actually found that the sex ratio  of bird populations can have a big impact on   how often birds divorce, and when you have a lot  of females per male, birds will often split up.

The reason for this is essentially just  because there’s a ton of choices for the   males, so if you’re not gelling with your current  partner it’s easy to swap them out for a new one. Again, not talking about humans. But before we get to the other reasons birds   go their separate ways, we  have to take a quick break.

This SciShow video is supported by Brilliant:   the online learning platform designed to  make you a better thinker and problem solver. If you’ve been saying that  you’re not a math person,   consider that you might be a  different kind of math person. Maybe memorizing formulas works for some  people, but Brilliant offers a different   approach based on problem-solving, in  which everyone can be a math person.

Brilliant guides you to “aha” moments, helping you   develop the intuition and problem-solving  skills to figure things out on your own. With Brilliant, the way we learn math  doesn’t have to be so confusing and hard. To learn for free with Brilliant for a  full 30 days, go to brilliant.org/scishow,   scan the QR code onscreen, or click  on the link in the description.

They’re also giving you unlimited daily access   to everything on Brilliant with 20%  off an annual Premium subscription. It’s not always the  males initiating a divorce. Female birds of various species may actually  attack and harass currently partnered females   to force them to leave their mate –  all so the new female can move in.

Of all things it’s believed  to be a tactic of kiwis,   those flightless fluffballs,  leading to high divorce rates. And in our friends the warblers, it was also  suggested strong couples may last as much from   their ability to protect their bond and their  territory as from their reproductive success. On the other hand – or wing – the  opposite was found in great tits.

Males who hung out with fewer females  in their winter flocks actually had a   much higher rate of divorce than  those who hung out with more. This was suggested to be due to the males  just grabbing an available female who might   not have been the best choice, leading to  him to divorcing her later after the poor   reproductive performance we now  know is so important for birds. Perhaps a little depressingly too, in some  cases you can actually see the break up coming.

But then again, can’t you always? And it’s for reasons that are pretty relatable. Great tits that spent less time with each  other in the winter period were a lot   more likely to divorce in the spring  before the mating and laying period.

Faithful pairs were together  a lot and built their bond,   while pre-divorcees just  let themselves drift apart. Further study can be done here too,   as the authors did muse whether such birds  were behaviorally predisposed to split apart. The couples’ life isn’t for everyone after all.

But some of the time, it’s not the  partnership, or the quality of your partner. Well, I guess it is, but more  so their ability to survive. In some birds, they divorce a lot because  they die a lot, so the odds of your   partner being alive in a year’s time for  the next breeding season are pretty slim.

And in the ever competitive game of life,  you just can’t afford to wait for them. At the same time, that high mortality  rate means there’s a lot of unpaired   birds around whose partners kicked the  bucket and who are looking for a fling. So they’re really lacking that dating  infrastructure to ever start something long term.

Well, I guess you can at least say they’re  living every day like it’s their last. Because it just well might be… At the end of the day,   birds have practical reasons both for  staying together and for splitting up. No matter how romantic we might be about  that penguin or albatross couple finding   each other after months apart, it’s  all about passing on their genes.

And learning about what makes them split up can be  as interesting as what makes them stay together. I am still waiting on that bird divorce  court daytime talk show, though. [♪ OUTRO]