Now let's pause for a second and point out some similarities between humans and zebra finches. Like many humans, zebra finches pair up socially for life. In other words, they form "marriages" based on child rearing, and they'll stick to one of those forever.
But like humans, that doesn't necessarily mean they're sexually monogamous. Both male and female zebra finches are known to seek out sex elsewhere, to varying degrees.
And also like humans, zebra finch females seem to have very singular taste. There isn't some single quality that makes a male zebra finch inherently more attractive to all the ladies — every female zebra finch will choose a mate based on her own criteria.
None of this is to say that research on zebra finch love is at all applicable to human behavior, of course. It's just really neat.
Okay, so now that you know everything you ever wanted to know about zebra finch dating, back to the study: The female finches were given time to choose mates. Half the couples were kept intact, but the other half were split up and put into arranged courtships with random suitors.
It's not surprising that the birds who picked their own mates had more reproductive success. But the love-match offspring were a staggering 37 percent more likely to survive than their counterparts.
The researchers observed more infidelity (first in the females, then in the males) in the artificially paired mates, even though males payed just as much attention to their females when they'd been paired at random. There were fewer instances of copulation (so fewer fertilized eggs overall) and less attention paid to newly hatched eggs, leading to high mortality rates in the early days after a hatching.
The researchers believe that the lack of reproductive success was due to behavioral problems, not genetic incompatibility. When females couldn't be with a male they found attractive — or, perhaps, when they were traumatized by the loss of a chosen mate — they didn't respond to their partner's affections, leading to discontent in the nest.
The experiment didn't really show why zebra finches pair up based on a female's individual tastes. But whatever made the birds evolve to behave this way, it seems to matter quite a lot.