Photograph by Sarah Darnell, Science Faction/Corbis
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A barn owl flies in Norfolk, England.
Photograph by Sarah Darnell, Science Faction/Corbis

Why Do Barn Owls Divorce?

While these “divorces” may mean sacrificing quality for quantity, both sexes can benefit from the split.

Love is a fickle thing—even in barn owls. These normally monogamous birds sometimes call it quits and move on to new partners—nearly a quarter of the time, in fact, says a new study published April 28 in the Journal of Evolutionary Biology. Among people in the U.S., the divorce rate is about 40 percent.

And while these “divorces” may mean sacrificing quality for quantity, both sexes can benefit from the split.

On a faithful note, barn owls tend to divorce only when breeding isn’t going well—for example, if there are only a few eggs laid or not many surviving chicks. When a pair is making a lot of babies, the birds remain quite loyal—and that chick-making relationship only gets better with time because the two mate more often, potentially maximizing the size of the family long-term.

Sometimes, It’s Splitsville

Amélie N. Dreiss and Alexandre Roulin, of the University of Lausanne, Switzerland, studied a population of free-living barn owls in western Switzerland for 24 years, observing how the pairs bonded and how many babies they had.

Barn owls are productive parents, often laying two broods per year with up to 11 (an average of six) eggs per brood. (Take National Geographic’s backyard bird quiz.)

But if there’s a year where they don’t have many babies, either partner might choose to seek a new mate.

Among the 634 owl pairs studied, 23.5 percent divorced: 166 pairs stayed together and 51 split, with males tending to “get the house,” meaning they stayed at the original breeding site.

Most in the divorce group had given the relationship just one year before separating (only a small percentage stayed faithful for multiple years—one couple really gave it a go, staying together for six years before giving up).

Who Leaves Whom?

In this species, very few animals “cheat”—so getting divorced is the only way to switch partners.

Because the birds are nocturnal and much happens after dark, it’s hard to know for sure which sex more often initiates the split, the scientists say. (Watch a video of night owls.)

Females tend to leave the nest after divorce, though some might be pushed out rather than choosing to go. What is known is that younger males are more likely to divorce than older ones are.

Roulin says that’s not because young males aren’t ready for commitment, but rather “it takes time to find the best mate.”

“A male may not have other choice than to divorce when he is young” in order to secure the most suitable sexual partner.

Looks Aren’t Everything

As for choosing partners, male barn owls prefer females with more and larger black spots on the tips of their feathers, though why exactly that’s considered better is unknown.

But after divorcing, the separated males often pair up with a younger, “lower-quality” bird (one with less black coloration)—suggesting that their reason for divorce isn’t to find a “superior” partner. (Also see “Wild Romance: Weird Animal Courtship and Mating Rituals.”)

“The cost of divorce for males, then, is to repair with a less sexy female,” Roulin says.

In this species, then, compatibility matters more than good looks. Males were typically better sexually matched with the new bird, so that breeding produced more chicks. Same went for females (who, unlike males, didn’t lower their standards when seeking a second partner): They usually fledged more chicks with a new mate than they had with the old.

Tight Families Thrive

Though divorce has its reasons in barn owls, the study authors note that chick survival was highest of all in families in which the parents were long-term, committed partners.

So if it takes a few tries and a few broken hearts, the goal is to find a truly compatible mate and then make babies, hanging in there for the duration. Not unlike the goal of another species we know.

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