Gorilla mistakenly believed to be male gives birth at Columbus Zoo

July 22 (UPI) -- A gorilla who zookeepers had thought to be male was only discovered to be female when she was found holding her new baby girl.

Zookeepers at the Columbus Zoo in Ohio said in a statement that the 8-year-old Sully, a western lowland gorilla, has lived at the facility with her mother and fellow troop members since 2019. For five years, the zoo believed she was a male.

"It's hard to tell the sex of younger gorillas. Until about age 8, males and females are about the same size, and they don't have prominent sex organs," the zoo said in its statement after Thursday's birth

"As gorillas age, they become sexually dimorphic, meaning males and females look very different. However, males don't develop their characteristic large size, silver backs and large head bumps -- called sagittal crests -- until age 12 or later."

Zookeepers described Sully as a "young and healthy animal" who did not need any procedures or medical care that would have led to the discovery sooner. The gestation period for a gorilla is about 8 1/2 months, meaning she became pregnant late in the fall.

Gorillas rarely show outward signs of pregnancy because the newborns are smaller than human babies and gorillas naturally have large abdomens.

"The troop is supportive of Sully and the infant, and they will remain as a social group," zookeepers said. "The infant appears to be healthy, and first-time mom Sully is taking good care of her."

Zookeepers have not yet approached the infant, also a girl, to allow time to bond with her mom. Eventually, veterinarians will approach to conduct a wellness exam. The zoo will also conduct a DNA test to determine the baby's father.

Sully and the infant live in a troop that has three males led by 39-year-old silverback Mac.