Sumatran Rhino Mom and Daughter Are Both Pregnant, and Mom Could Set a Record

Two of the rarest large animals on Earth are pregnant at the same time, and they happen to be mother and daughter. Presumably nobody is fighting over the good crib.

Ratu, a 26-year-old Sumatran rhino, and her 10-year-old daughter, Delilah, are both expecting at the Sumatran Rhino Sanctuary in Way Kambas National Park, in Indonesia's Lampung province.³ The sanctuary is home to 10 Sumatran rhinos, according to the Jakarta Post, so this is a big week for roughly a fifth of the residents.³

Indonesia's Ministry of Forestry and Yayasan Badak Indonesia, the foundation that runs the sanctuary, shared the news in early October during World Rhino Day events at Taman Safari Indonesia in Bogor.²⁵

"The pregnancies of these two Sumatran rhinos are not only good news for Indonesia, but also for the world," said Ahmad Munawir, Director of Species and Genetic Conservation at the Ministry of Forestry.⁵

Due Date: Around May 2027, So Get Comfortable

At the time of the announcement, Ratu was about 238 days along with her fourth calf, fathered by a male named Andalas. Delilah was about 251 days along with her second, fathered by a male named Harapan.⁵⁶

That sounds like a lot of days until you learn that a Sumatran rhino pregnancy lasts about 15 to 16 months.³ Both moms are roughly halfway there. Both calves are expected around May 2027.²⁶

Until then, veterinarians, keepers and sanctuary managers are keeping a close eye on both pregnancies all the way to delivery.⁵ These are pregnancies, not births, and caution is warranted. Some of Ratu's earlier pregnancies ended in miscarriage.

Ratu Is Going for the Record

Ratu's career in conservation began in 2005, when she wandered out of the forest and into a village in Way Kambas and was taken in by the program.³ It was not a planned job interview, but it worked out.

If her fourth calf is born healthy, Ratu would become the first known Sumatran rhino to give birth to four calves. The current record of three belongs to a female at the Cincinnati Zoo.²

Delilah has her own first. She was born at the sanctuary in 2016, and in November 2023 she gave birth to a male calf named Indra. That made her the first captive-born female Sumatran rhino to successfully produce offspring.⁴ The Way Kambas program has produced five calves since 2012, with Indra the most recent.⁴⁵

A Family Tree With Very Few Branches

Every calf matters because there are so few Sumatran rhinos left. The IUCN lists the species as critically endangered, with fewer than 80 in the wild.³ An IUCN Asian Rhino Specialist Group assessment cited by Mongabay puts Indonesia's wild population even lower, at 34 to 47 animals scattered in isolated groups.²

Sumatran rhinos are loners. That is a fine lifestyle until it's time to start a family and the nearest available rhino lives on the far side of a broken-up forest. Habitat fragmentation makes it harder for wild males and females to find each other at all.²

Captive breeding has its own puzzle. Andalas and Harapan are full brothers, both born at the Cincinnati Zoo, in 2001 and 2007. All the males in the program are related, and Delilah's calf was sired by her paternal uncle.²¹ Inbreeding, meaning breeding between close relatives, can weaken a population's health over time. Sanctuary specialists try to pair the least closely related animals, but with so few rhinos in human care, the options are slim.¹

So this is hopeful news, not proof that wild Sumatran rhinos are bouncing back. It is still good news.

"Ratu and Delilah's pregnancies represent two more individuals that can help bring Sumatran rhinos back from the brink of extinction," said Nina Fascione, executive director of the International Rhino Foundation.⁴

Next comes the long wait until spring 2027. If all goes well, Way Kambas gets two new calves, and Cincinnati gets to keep its rhinos famous in a new way, as the hometown of two very busy brothers.