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John Kortas courtesy of Lincoln Park Zoo
Baby white-cheeked gibbon, Sai, and mother Burma at Lincoln Park Zoo.
Lincoln Park Zoo welcomed its newest ape Tuesday, a bouncing baby boy gibbon.
Part of the critically-endangered ape species of southeastern Asia, the male white-cheeked gibbon was born at the zoo in January but his sex was unknown until Tuesday.
Zookeepers also named the baby Sai (pronounced "sigh") which means "son" in Taiwanese.
"He is the third offspring," said Lincoln Park Zoo Curator of Primates Maureen Leahy. "All sons for the mother Burma and father Caruso."
Although Sai was born a golden tan color, he will turn black and have white fur on his cheeks at the age of two.
"Sai has been transforming right before my eyes over the last three months," said Leahy.
Already the baby gibbon's fur is starting to darken and his teeth have grown in, said Leahy. He is also showing an independent streak, venturing away from his mother and testing his long arms on vines.