These Lady Birds Will Not Hesitate to Divorce Their Loser Husbands

Even birds cheat, but they swear they can explain.
July 21, 2016, 11:00am
Still from Bambi, Walt Disney Productions, 1942. Image: Pyxruz

When it comes to love and marriage, female purple-crowned fairy-wrens (Malurus coronatus) are more than a little flighty. Is your husband about to die? Leave him. Found a hot new sidepiece? Seeya later. Fancy some better-looking digs? Bye!

This tiny bird species may be monogamous, but it boasts one of the most cutthroat dating scenes in the animal kingdom. According to a study published this week in Behavioral Ecology, one in five relationships between purple-crowned fairy-wrens ends in "divorce." And most of the time, females are the ones breaking hearts (and nests).

"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," lead author Anne Peters, an associate professor of biology at Monash University, told Phys.org. "With divorce they get a different partner and a different territory. The territory seems to be more important than the partner."

Male and female purple-crowned fairy-wren. Image: Wikipedia/P Barden

To humans, the fairy-wren's survival strategy may seem brutal, but in an ecological context, it makes a lot of sense. Fairy-wrens are endemic to the wetlands of northern Australia, and tend to nest close to the ground. Their primary threats are habitat loss, overgrazing by sheep and cattle, and wildfire. According to the study's co author, Nataly Hidalgo Aranzamendi, these endangered birds live in "a harsh, unpredictable environment where 80 per cent of nest attempts end in failure," so females would benefit from the ability to find new mates and better territory. It's not infidelity, it's just fitness.

"We believe divorce is a female strategy to improve reproductive success in the long term, and the immediate benefit is a better territory," added Aranzamendi.

Fairy-wren breeding occurs year-round, and couples will live in family groups of up to six individuals. Females usually lay three eggs at a time, and won't send their chicks off for several years. The species got its name from the vivid purple crown that males develop during the breeding season.

Overall, promiscuity is fairly common in nature. Among mammals, nearly 90 percent of species have multiple partners and "cheat." A mere three to 10 percent of mammals are monogamous, and as this new study proves, even the most faithful can falter.

It's estimated that only 10,000 purple-crowned fairy-wrens remain in Western Australia's Kimberley region. Biologists are currently trying to map the bird's habitat, so as to better understand where populations are flourishing, and where they need conservation assistance.