SYRACUSE, N.Y. (AP) — Two baby patas monkeys were born weeks apart at the Rosamond Gifford Zoo in upstate New York and are being raised by keepers after their mothers showed a lack of maternal instinct, a zoo official said Thursday.

Iniko gave birth to Sisu on April 26 and Iniko’s older sister, Kasi, also gave birth to female, Mushu, on May 11. The wide-eyed, big-eared babies were fathered by the patas troop leader, Mac, making them half-sisters.

The Rosamond Gifford patas troop lives at the zoo the way the highly social species does in the wild, in a group featuring one male and several females, according to the zoo. The survival rate for patas monkeys is relatively low in the wild because young monkey mothers often can’t or won’t raise their young.

Zoo handlers were on the lookout for signs that Iniko and Kasi needed help and stepped in when it appeared they did. The staff is rearing the half-sisters together, drawing from the experience of raising Iniko after her mother died during delivery in 2020.

“Given the adversity that this species faces with reproduction, Iniko and Kasi’s babies are an exceptional contribution to the zoo’s patas monkey troop and the North American population,” zoo Executive Director Ted Fox said in a news release.