Watch: Two newborn patas monkeys being hand-raised at New York zoo

Aug. 9 (UPI) -- A New York zoo announced the births of two patas monkeys -- half-sisters -- who are now being hand-raised by keepers.

The Rosamond Gifford Zoo in Syracuse said a monkey named Iniko gave birth to a baby girl named Sisu on April 26, while her older sister, Kasi, gave birth to a girl named Mushu on May 11. Both babies were fathered by Mac, the leader of the zoo's patas troop.

The zoo said in a news release that both monkey mothers "struggled to demonstrate maternal instincts necessary to raise their young," so both babies are being hand-raised by zookeepers.

"We are so glad to welcome these primate newborns to our zoo, and are fortunate to have such an amazing zoo to call home," County Executive Ryan McMahon said. "The animal care team's diligent work has ensured little Sisu and Mushu have a safe and healthy future."

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Zoo officials said patas monkeys have a high infant mortality rate in the wild, and it is not uncommon for mothers to be "uninterested in or incapable of raising their young."

"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. "Since the babies are so significant, our primate specialists took action to protect these little patas babies and safeguard their health so we can reach our ultimate goal of having them eventually join the rest of our patas troop."