In the idyllic setting of the Wildfowl and Wetlands Trust in Slimbridge, 325 hectares of wetland in Gloucestershire, south-west England, alive with water voles and dragonflies and the world’s largest collection of swans, geese, and ducks, live a pair of exuberant gay flamingos named Carlos and Fernando.

Together for six years, they have raised three chicks after stealing eggs from other couples, feeding them by producing milk in their throats. This week, the pair was given the responsibility of raising a newly hatched flamingo that has been rejected by its mother.

The question of whether animals can be homosexual has been extensively explored in recent times. In 1999, Biological Exuberance: Animal Homosexuality and Natural Diversity, the result of 10 years of research by Bruce Bagemihl, documented many cases of homosexual behaviour in animals. It has been shown in 1,500 species, from rams to guinea pigs, chaffinches to warthogs.

Last year, an exhibit at the University of Oslo showed 51 examples of animals displaying homosexuality — from female bonobos rubbing their genitals together to male killer whales riding the dorsal fins of other males.

In the avian world too, nearly a quarter of black swan families are parented by homosexual couples, the males sometimes mating with a female simply to have a chick. Once the egg has been laid, the female is chased away and the males hatch it. Homosexuality in flamingos is also relatively common. In the case of Carlos and Fernando, both assume the male roles during the courtship ritual — preening, strutting and waving their heads vigorously from side to side.

There are other famous gay animal pairings. Central Park zoo in Manhattan, New York, had a famous pair of gay chinstrap penguins named Roy and Silo, who were inseparable. They lived together for more than six years. They entwined their necks, vocalised to each other, had sex and, at one time, for want of an egg, tried to incubate a rock in their nest. Later, the pair hatched a donated chick, named Tango, but sadly the couple separated in 2005. Silo has since found love with a female penguin named Scrappy, while Roy remains single.