When penguins Chupchikoni and Suki coupled up two years ago, zookeepers at the Ramat Gan Zoological Center in Israel didn’t think much of it. After all, penguins typically mate for life.

But a blood test conducted 20 months later revealed that there was something special about the relationship: Chupchikoni and Suki are both females.

“They're living together, they have their own nest,” zookeeper Mor Porat told NBC News’ Yara Borgal. “We even saw them trying to mate a few weeks ago.”

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And although they don’t share a chick of their own, the penguin couple is still preparing for a little one.

“They're also acting as if they were nesting,” Porat said. “Obviously they don't have their own egg, but they’re doing everything like a couple of male and female.”

While they’re not the first same-sex penguin couple to make headlines (remember Buddy and Pedro at the Toronto Zoo?), they are the first female penguins to pair up at the zoo. Females are thought to couple with each other less often than males.

“I think it’s the first time we’ve actually seen two females,” Porat said. “It’s actually very exciting.”

Zookeepers initially surmised that the same-sex pairing was the result of a lack of males on exhibit, but they eventually determined that the match was a spontaneous one.

Visitors, who must be told about the unusual relationship because males and females look very similar, have been delighted by the discovery.

“When it comes to animals things are much simpler than with humans because everyone accepts them,” Borgal said.