The mothers, Electra and Viola, are one of three gentoo penguin couples to welcome a new chick at the Oceanogràfic València aquarium this breeding season so far, according to a press release. That is not a large number compared to other years, but the fact that one of those chicks will be raised by two moms makes this breeding season unique.

"Even though the formation of same sex partnerships is common in more than 450 animal species, both in captivity and in the wild, this is the first time it has happened at our aquarium," the Oceanogràfic València wrote in a Aug. 17 Facebook post announcing the birth. "So, welcome to the world, little one!"

Electra and Viola are two of the 25 gentoo penguins being cared for at the Valèncian aquarium. Their journey to motherhood began when the pair started to build a nest of stones together. Their caretakers then gave them a fertile egg from another pair to care for.

"Electra and Viola carried the entire reproduction process forward with success and now have their first baby," the aquarium wrote.

Gentoo penguins build nests out of pebbles that can be as large as 20 centimeters (approximately 8 inches) across. Couples usually take turns incubating the eggs, which hatch after around 38 days. The baby chicks then gain their independence 75 days after hatching.

While Electra and Viola are the first same-sex penguin pair to raise a baby together at the Oceanogràfic València, similar families have formed at other zoos and aquariums.

In 2018, two male gentoo penguins at Sea Life Sydney Aquarium in Australia began to build a nest together, as CBS News reported. Caretakers first gave the penguins, named Sphen and Magic, a practice egg to care for. When the pair proved themselves attentive fathers, their caretakers presented them with a real egg to hatch.

In September of 2019, a male gentoo pair at Sea Life London announced they would be raising their child without a gender, the New York Post reported.

"What makes us really proud at the aquarium is the success of Sea Life London's gentoo breeding program and the amazing job of same-sex penguins Rocky and Marama who took the chick under their wing and raised it as their own," the aquarium's general manager Graham McGrath said at the time.

It isn't only gentoo penguins who form same-sex parenting pairs in captivity. Two male African penguins at the DierenPark Amersfoort zoo in the Netherlands kidnapped another pair's egg in November to hatch and raise as their own, the New York Post reported at the time.

"Homosexuality is fairly common in penguins, but what makes this couple remarkable is that they have gotten hold of an egg," zookeeper Marc Belt said.