A pair of male penguins who have nested together for six years apparently broke up when a female penguin became available, say caretakers at the San Francisco Zoo.
Harry and Pepper, a pair of Magellanic penguins, started nesting together in 2003 and incubated an egg last year.
However, zoo keepers confirmed in early July that Harry has been nesting with a female penguin, Linda, for several months, said a report in the San Francisco Examiner.
Linda and Harry became friendly shortly after her long-term partner, Fig, passed away in the winter. Within a week of Fig's passing, Harry was spotted in Linda's burrow.
Harry and Pepper had a violent confrontation and zookeepers removed Pepper from the penguin colony. He has since been reinstated, but zookeepers say they're concerned the upcoming penguin moulting season in late July could cause upheaval among penguin couples.
Zookeepers say it's not the first time Linda has been involved in such a triangle. Several years ago, she left her longtime partner and moved in with Fig shortly after his partner passed away.
Earlier this year, zookeepers at Germany's Bremerhaven zoo gave a same-sex pair of Humboldt penguins an egg to incubate. The egg hatched in early June and the penguins, named Z and Vielpunkt, are raising the chick.
The pair is one of three same-sex pairs of Humboldt penguins at the zoo. That means almost one-third of the zoo's 20 penguins who have attempted to mate exhibit homosexual behaviour. Same-sex penguin pairs have also been observed at zoos in Japan, Scotland and New York.