I’m sure this pains the people who take offense at the true-life tale And Tango Makes Three, but heterosexuality is not the rule in the animal world. There are hundreds of species, from bison to bunnies to beetles, that pair off in same-sex couples. (And then there are bonobos.) Birds often pair off this way, too. And now a study of zebra finches, published in Behavioural Ecology and Sociobiology, has found that the bonds between same-sex couples can be just as strong as those in heterosexual birds.

Zebra finches, which live in grasslands and forests of Australia and Indonesia, form pairs that last a lifetime. The males sing to their partners, and the two share a nest and clean each other’s feathers. They nestle together and greet each other by nuzzling beaks.

Researchers raised groups of zebra finches in same-sex groups, all male and all female, and in each group the majority of birds paired up. They interacted frequently and often preened their partners. And they weren’t aggressive to each other as they were to other birds in the group. These are all characteristics found in heterosexual finch couples.

The scientists then tested the bonds in the male-male couples by introducing some females to the party. A few birds were tempted by the ladies, but when the females were removed, the male-male couples reformed.

“A pair-bond in socially monogamous species represents a cooperative partnership that may give advantages for survival,” lead author Julie Elie, of the University of California Berkeley, told BBC News. “Finding a social partner, whatever its sex, could be a priority.” Having a mate could help a bird to find food or repel predators.

Elie also told BBC News, “relationships in animals can be more complicated than just a male and a female who meet and reproduce, even in birds.” Or in humans.