Jay Petersen, curator of carnivores and primates at the Brookfield Zoo, said 3-year-old male white-cheeked gibbon Thani recently discovered how to cross from his display area to the orangutan display area, where he struck up a friendship with 4-year-old female Bornean orangutan Kekasih, the Chicago Tribune reported Friday.
"They have become playmates," Peterson said. "We've been watching them closely, but so far their interactions are positive, so we will let things be."
He said Kekasih's mother, Sophia, 32, has also taken a liking to Thani. Peterson said the gibbon has been seen jumping on Sophia's back, leading her to smile at him.
Peterson said a gibbon and an orangutan previously struck up a friendship at the zoo in the 1980s.
"It's a learning experience for us," Petersen said. "It shows us how they adapt to their surroundings while learning to interact with other primates."