Zookeepers surprised when gorilla thought to be male gives birth

Last week at the Columbus Zoo and Aquarium in Ohio, zookeepers discovered that one of the western lowland gorillas was holding a baby. Not only did they not know that eight-year-old Sully had been pregnant, they also thought she was a male, making this quite the shock — but a welcome one.

Sully (Sulaiman) was born at the Milwaukee Zoo. She and her mother came to the Columbus Zoo in 2019 (half-sister Zahra was already there). After the birth of the female infant last week, keepers realized she had been misclassified as a male. The zoo’s blog explains that it’s difficult to tell the sex of younger gorillas because there’s no size difference and no prominent sex organs are visible. Males don’t develop their larger size, head bumps, or silver backs until they are at least 12 years old.

Keepers and veterinarians at the zoo keep a hands-off approach to the care of gorillas and Sully arrived healthy, so she did not need any medical procedures that required anesthesia prior to the birth. Otherwise, the gender discovery might have been made more quickly.

Not knowing a gorilla is pregnant isn’t unusual, either.

MORE: The National Zoo welcomed a new baby gorilla and the photos are precious

“Gorillas rarely show outward signs of pregnancy because the newborns are smaller than human babies and gorillas naturally have large abdomens,” the zoo’s blog explains.

According to the zoo’s social media, the mom and baby are bonding with each other and the other gorillas. They have access to different areas on exhibit and behind the scenes and may choose where to spend their time, and the habitat is now open to the public for viewing.

Gorillas have a gestation period of about 8.5 months, so Sully became pregnant last fall. It’s unclear which gorilla is the father of the infant. The troop is led by 39-year-old silverback Mac, but also includes two younger males  — Kamoli, age 10, and JJ, age 6. There are five other females in the group, and the Columbus Zoo also has a separate family group of one silverback and four females. Zoo staff will eventually do a DNA test to determine the paternity of Sully’s offspring.

Columbus Zoo says it is “thrilled” about the news, since western lowland gorillas are a critically endangered species with a population of about 100,000. According to the International Union for Conservation for Nature’s Red List, threats to the species include capture for the bushmeat trade, deforestation, climate change, and habitat loss from agriculture, mining and transportation.

The zoo has a history of contributing to gorilla conservation. In 1956, it became the first zoo in the world to welcome a baby gorilla birth. It has pioneered gorilla fostering programs and supports several conservation projects in Central Africa. It also founded Partners in Conservation, which raises funds to protect African wildlife.

Congrats to Columbus Zoo and new mom Sully!