Two male penguins entrusted with the care of a fostered egg have welcomed a tiny sub-Antarctic Gentoo chick into the world, Sydney's Sea Life Aquarium said today.

The pair, Magic and Sphen, made headlines around the world this month when aquarium staff gave them the egg, following a successful trial with a dummy egg.

The yet-to-be-named chick, weighing 91 gm (3.21 oz), was born on the evening of October 19 and is the first sub-Antarctic penguin born at the aquarium.

Magic and Sphen, two male penguins who built a nest and fostered an egg together, interact with each other in Sydney's Sea Life Aquarium, Sydney, Australia, in this still image taken from an undated video obtained from social media. Photo: Reuters

The couple, who formed a bond before the 2018 breeding season, doted on the adopted chick, said Tish Hannan, an aquarium official.

"The first 20 days of a penguin chick's life are the most vulnerable, so it is extra-important the chick is very happy, healthy and well fed by his parents," she added.

Magic and Sphen had placed the egg on small nesting rings built with pebbles and shared duties, with one patrolling for possible threats, while the other kept the egg warm.

There is little difference between opposite-sex and same-sex rearing among Gentoo penguins, which share parenting and feeding responsibilities equally, Hannan said prior to the birth, adding that the example was not the first among zoos across the world.

A children's book, "And Tango Makes Three", based on the real story of two penguins at New York's Central Park Zoo who reared their own chick, drew acclaim from some for its depiction of non-traditional family structures.

It was also among the titles Hong Kong pulled from bookshelves in public libraries this year, following pressure from anti-gay groups, the South China Morning Post newspaper has said.