A prairie vole photographed in Lincoln, Nebraska. Unlike most rodents, prairie voles pair up, build a nest, groom each other, and raise their young.
10 amorous animals that mate for life
Every day is Valentine's Day for these monogamous species. See photos of wild sweethearts from National Geographic's Photo Ark.
What makes an animal want to stick with another for life?
Monogamy may not be commonplace among all of Earth's creatures, but for a select few, it's the secret to survival.
Take the prairie vole (Microtus ochrogaster), for instance. Unlike most rodents, prairie voles pair up, build a nest, groom each other, and raise their young. (Why male prairie voles are changed forever when they settle down.)
Their monogamous behavior is partly rooted in the sparse grasslands of the United States and Canada. The animals must fight for limited resources and breed as much as they can during a life span that lasts only a year or two—and they can accomplish more as a team.
But there's more to this love story. Experts say certain brain chemicals play a role in forming bonds among prairie voles—more so than in other rodents. (Explore the genetics of prairie vole commitment.)
Still, love is complicated, even for these furry models of matrimony.
Prairie voles are considered "socially monogamous" but not "genetically monogamous," according to William Kenkel, a postdoctoral researcher at the Kinsey Institute in Indiana.
Occasionally, either the male or female may stray and mate with a stranger. For now, researchers are stumped as to why.
"They are not 100 percent faithful, which might even make them a better model for human behavior," Kenkel said.
Throughout the animal kingdom, scientists have found examples of critters that only have eyes for one mate, while others prefer the status of mostly monogamous.
Whatever the case for them, the animals in this gallery seem to believe in aspects of monogamous bliss.