Birds can have gay relationships that last for life, say researchers.

They found that if isolated from the opposite sex, same sex birds will pair off with each other.

The scientists studied young zebra finches, which are known for forming lifelong relationships.

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© Press AssociationComfortable together: A study showed zebra finches sang to and preened each other just like heterosexual pairs.
When raised in same-sex groups, more than half the birds paired up together. When females were then brought into the male group, five out of eight pairs of males ignored them and stuck with their male partner.

As in their relationships with the opposite sex, they were found to be as 'attached and faithful', perching side by side, nesting together and greeting each other by nuzzling each other's beaks.

Lead author Dr Julie Elie, from the University of California, Berkeley, said: 'Relationships in animals can be more complicated than just a male and a female who meet and reproduce.

'My observations of [them] led me to this surprising result: same-sex individuals would also interact... like male-female pairs.'

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© Still PicturesBest mates: In captivity, there have been cases of male penguins forming long-term bonds
Her team, whose study is published in the journal Behavioural Ecology and Sociobiology, believes the same-sex pairings could be a strategy for survival, the birds teaming up to defend resources and fight predators.

'A pair-bond in socially monogamous species represents a cooperative partnership that may give advantages for survival,' Dr Elie continued.

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

Dr Elie said there were several examples of same-sex pairing in the avian world.

In monogamous gulls and albatrosses, it gave females the chance to breed without a male partner.

'Female partners copulate with a paired male then rear the young together,' Dr Elie explained.

In captivity, there have been at least two cases of male penguins choosing each other over a females companion.

Two male chinstrap penguins in Manhattan's Central Park Zoo, named Roy and Silo, bonded and paid no attention to females in their enclosure for at least a year.

They built a nest together, incubated and hatched a fertilised egg donated to them by one of the keepers.