A study has found that zebra finches can form lifelong same-sex relationships.

Researchers at the University of California, Berkeley, chose the species to study because zebra finches are known for forming permanent monogamous relationships.

They found that when the birds were raised in same-sex groups, over half of the males formed same-sex couples. Even when females were introduced to the group, five out of the eight male couples ignored them and continued their relationships.

Researchers also found that the same-sex couples showed the same behaviour to each other as opposite-sex couples did, including nesting together, singing to each other, perching side by side and greeting each other.

Lead researcher Julie Elie told BBC Nature: “The research showed relationships in animals can be more complicated than just a male and a female who meet and reproduce, even in birds.

“A pair-bond in socially monogamous species represents a cooperative partnership that may give advantages for survival.

“Finding a social partner, whatever its sex, could be a priority.”