Two male penguins who have paired up as a "same-sex couple" have become so good at nesting that zookeepers in Sydney have given them a real egg to look after.
Sea Life Sydney said they had been watching "inseparable" gentoo penguins Sphen and Magic become a "great team" during this breeding season.
Initially the pair were "constantly seen waddling around and going for swims together" and then they began to build a collective nest of pebbles.
They gathered more than any other couple, prompting the aquarium to provide a dummy egg for them to look after.
"They were absolute naturals and displayed great care for their egg, so much so, the team at Sea Life Sydney fostered a real egg to them from another couple who had two," the aquarium said.
The pair are incubating their charge well enough that "there are often days where the egg cannot be seen," it added.
But there is some room for parental improvement, with staff saying younger penguin Magic is still mastering the skill.
This is not the first time same-sex penguin couples have adopted eggs in captivity, with a handful of zoos worldwide reporting similar cases.
In 2009, two male penguins -- Z and Vielpunkt -- successfully hatched and reared a chick that was was rejected by its heterosexual parents at a zoo in Berlin.
Before them came Roy and Silo, two male chinstrap penguins at a zoo in New York who were spotted frequently trying to mate with each other. After they tried to incubate a rock, zookeepers gave them a foster egg which they successfully hatched. Their foster chick, a female called Tango, eventually paired up with another female.