Many birds are known for their monogamy and mate loyalty; some species even choose a single partner to mate with for life. But researchers are discovering that the reality of avian marriages aren't always so rosy as they might first appear.

Take, for instance, purple-crowned fairy-wrens, a highly territorial species endemic to Australia. Researchers studying these largely-monogamous birds have found that as many as one in five pairs will end in divorce, and that it's usually the females that initiate the separation, reports Phys.org.

"Females exhibit long-term planning and are more likely to end their relationship when the opportunity for a better territory arises," said lead researcher Anne Peters. "We found females were prepared to wait, sometimes up to three years, for a good vacant spot to come up — where the female owner has died or moved on."

The surprising behavior shows that it's the females who are really calling the shots in these relationships. Interestingly, female birds were also witnessed regularly kicking younger females out of their territories, to stake firmer claim on their turf. This is a role-reversal of the sexes, compared to what's commonly observed in many other species.

Females engage in affairs too, and these affairs are often indicative of a future divorce, where the female leaves her partner for a male that occupies a more favorable territory.

"These females are sitting there, they're not happy with their partner or their territory; they have an affair on the side and they're more likely to divorce. With divorce they get a different partner and a different territory. The territory seems to be more important than the partner," Peters explained.

Before judging the shrewd behavior of these female fairy-wrens, consider that the birds live in a relatively harsh, unpredictable environment, where 80 percent of nest attempts end in failure. Favorable territory is in high demand, and there are real-life consequences of survival associated with territory. So divorce is a necessary female strategy to improve reproductive success in the long term, given the birds' social structure. When life and death are on the line, love and loyalty have to take a back seat.

The research shows how important habitat protection is for these endangered birds. It's crucial to ensure the species' survival, both in life and in marriage.