Tensing’s Pregnant!

Our 11-Year-Old Greater One-Horned Rhino is Expecting a Calf in Spring 2020

Earlier today, we celebrated World Rhino Day with some exciting news that we’ve been very anxious to share for a long time: Tensing, our 11-year-old greater one-horned rhino, is pregnant! Rhinos have one of the longest gestation periods of all mammals at an average of 470-480 days, so, while Tensing conceived in November 2018, her due date isn’t until spring 2020. Any animal pregnancy is cause for celebration, but this one is an especially big deal—and not just because of the size of the expected newborn, which may grow up to 6,000 lbs. as an adult.

“Tensing’s pregnancy is an incredible example of what Denver Zoo—and other zoos accredited by the Association of Zoos and Aquariums—do to ensure the survival of many vulnerable, threatened and endangered species,” said Brian Aucone, Senior Vice President for Animal Sciences. “This was a multi-year process that involved countless hours of care and training, and the cooperation of partner zoos.”

Read below to find out how we helped Tensing become pregnant, and why her pregnancy is so important to her vulnerable species:

A Rhino-Sized Effort

When Tensing first arrived at the Zoo in 2011, she was not trained to participate in an artificial insemination procedure, which eventually led to her pregnancy (side note: Bandhu, our 10-year-old resident male greater one-horned rhino had not yet reached maturity at the time). Our Animal Care team provided extensive training with a focus on positive reinforcement to teach her how to participate in her own care, including voluntary ultrasounds and, eventually, artificial insemination procedures.

Success did not come quickly or easily. Our Animal Science team led by Dr. Anneke Moresco—with assistance from Dr. Monica Stoops from the Center for Conservation and Research of Endangered Wildlife (CREW) at Cincinnati Zoo, now lead reproduction scientist at Omaha’s Henry Doorly Zoo and Aquarium—conducted 11 unsuccessful artificial insemination procedures with Tensing from 2014 to 2018. During that time, Tensing’s care team worked tirelessly to adjust her training and environment, while our Animal Science team diagnosed excess fluid in her uterus, a condition that might have prevented the embryo to implant on previous attempts. During the last AI, the team administered treatment to help with this condition.

On November 11, 2018, Drs. Moresco and Stoops attempted a 12^th artificial insemination procedure with sperm from Jontu, a 10-year-old male greater one-horned rhino from Omaha’s Henry Doorly Zoo and Aquarium. A voluntary ultrasound 10 days later suggested she was pregnant. Her pregnancy was confirmed 23 days after insemination by observing the embryo on ultrasound, and subsequent weekly voluntary ultrasounds have shown her fetus is healthy and has grown to roughly the size of a large watermelon. He or she is due in late March or early April 2020.

Not Out of the Woods

Once widespread, the population of greater one-horned rhinos—also known as Indian rhinos—plunged in the past as they were hunted for sport and viewed as agricultural pests. Strict protection efforts have helped greater one-horned rhinos recover to an estimated 3,500 individuals, far more than the 200 that remained when the species was on the brink of extinction due to hunting in the early 20^th century. Managed breeding programs within zoos also help to safeguard the species’ survival. There are currently 82 greater one-horned rhinos in North American facilities. But the species is still listed as “Vulnerable” by the International Union for the Conservation of Nature due to numerous threats in their native range of northeastern India and Nepal, including agriculture, poaching and land development.

Be sure to follow us on Facebook, Twitter and Instagram for regular updates on Tensing and to be among the first to know when her calf arrives. While you’re waiting, stop by Tensing and Bandhu’s home in Toyota Elephant Passage on your next visit, or book an Up-Close Animal Encounter to meet one of these prodigious pachyderms—and many other Denver Zoo residents—in person!