First Hippo Ultrasound Shows Pregnancy; How Zookeepers Managed It

CINCINNATI, OH — This isn’t a joke, though it reads like the setup to one: How do you convince a 3,200-pound hippopotamus to stand in a specific space, lean just so against a gate and remain perfectly still while an ultrasound procedure is performed to confirm her pregnancy?

The zookeepers at the Cincinnati Zoo pulled it off with aplomb. And yes, Bibi, a Nile hippopotamus, is pregnant. Zookeepers had hoped for as much when the 17-year-old Bibi and Henry, 25, got together last July in the zoo’s Hippo Cove.

Their copulation was widely observed, and zookeepers and others have since been watching since for telltale signs that Bibi was pregnant. Weekly ultrasounds began in August.

“Hippos are generally known for being very difficult to train and many folks were skeptical that we would be able to pull this off,” Jessye Wojtusik, of the zoo’s Center for Conservation & Research of Endangered Wildlife, said in the announcement.

How did the zookeepers do it?

Wojtusik credits an experienced, professional staff with making the milestone ultrasound diagnosis possible. They used positive reinforcement —Bibi's favorite foods — to condition her for the procedure.

It also helped that Bibi is a nice, well-behaved hippopotamus.

“Fortunately for us, Bibi came to Cincinnati with a very solid background in training from her dedicated keepers at the St. Louis Zoo, which made it easy for our team to develop the ultrasound behavior with her,” Wendy Rice, the head keeper of the zoo’s African animals, said in the announcement.

“Once she’s in position and holding steady, we keep the treats coming and Bibi is more than happy to cooperate,” Rice said in the announcement. “On a good day, she’ll hold her position for up to 15 minutes, giving us plenty of time to search for the baby.”

Dad-to-be Henry comes along for each ultrasound appointment.

Rice said he has been “an amazingly supportive and doting partner.” In general, he splashes around in his indoor pool nearby and occasionally bellows to Bibi, Rice said.

The gestation period for a Nile hippopotamus is eight months, so Bibi’s baby should arrive sometime in March. Zoo officials have begun baby-proofing the habitat and planning for the birth. Unless it’s unseasonably warm, Bibi will most likely deliver in her indoor pool.

She and Henry will be separated during the birth and for about two weeks after. In the wild, female hippos leave the group a couple days before birth and return with the calf 10-14 days later.

The first residents of Hippo Cove received a breeding recommendation from the Association of Zoos and Aquariums Species Survival Plan, the organization that monitors animal populations in Zoos. Henry has sired several calves, but Bibi will be a first-time mom. It’s been more than 75 years since the Cincinnati Zoo welcomed a Nile hippo calf.

Nile hippos, also known as river hippos or river horses, are vegetarians and can weigh as much as 4,000 pounds. Males are typically much larger than females. Although hippos spend much of their day in the water, they actually can’t swim at all. They float or walk along the bottom of the water.

Hippos are not endangered, but their populations are vulnerable to extinction due to habitat loss. A smaller species of hippo, the pygmy hippo, is endangered.

Photo by Dave Lundy via Flickr Commons: A nearly submerged hippopotamus at the Cincinnati Zoo.