A 25-year-old female Sumatran rhino has died at a sanctuary in Borneo, marking the extinction of the species in its native Malaysia.

The rhino, named Iman, had cancer, and state officials in Malaysia described the death as natural, according to the Star, an English-language newspaper in Malaysia. The paper reported that before her death, Iman had nearly died several times due to blood loss from her uterine tumors but was nursed back to health each time.

Iman’s death is a blow for the species, already among the most endangered in the world. Sumatran rhinos are “critically endangered,” according to the International Union for Conservation of Nature’s “red list,” meaning the species is just one category removed from extinction in the wild. Still, investments in breeding programs and scientific advancements with reproductive technology offer outside hope.

There are fewer than 80 Sumatran rhinos — sometimes called “hairy rhinos” — left in the world, with some estimates as low as 30, according to the World Wildlife Fund. Once native to rainforests throughout Asia, Sumatran rhinos now only live in the wild in Indonesia.

Repopulation efforts are complicated by a mix of human-driven factors such as building into the rhinos’ native habitats and the animals’ loner nature coupled with their long gestation periods, according to Terri Roth, vice president of conservation and science at the Cincinnati Zoo and Botanical Garden.

Courtship for Sumatran rhinos isn’t easy, either.

“What’s made breeding these rhinos so difficult is because they are so solitary; you can’t house males and females together, or else they’ll fight, and the pairing has to be timed to when the female is ovulating,” Roth told The Washington Post on Saturday. “What’s happened with the wild population, and such fragmented forests, is that they don’t come into contact often enough.”

Female Sumatran rhinos gestate a single calf for about 15 months and go long stretches without being pregnant. Infertile periods also mean reproduction issues can crop up in males and females, Roth said, noting that Iman already had uterine tumors by the time she was captured in 2014.

Though poaching has long been a threat to rhinos, Sumatran rhinos live deep in the forests and don’t travel in herds, making it somewhat more difficult for poachers to get to them. Disruption of their habitat due to palm oil harvesting and general development has been the bigger threat, according to Roth, who also directs the zoo’s Center for Conservation and Research of Endangered Wildlife.

“Locally, the populations [in Indonesia] have increased, so more and more, people are going into the forests for firewood or to build,” she said. “It’s difficult to balance the needs of the people and the wildlife needs

Iman’s death comes less than six months after Tam, Malaysia’s last living male Sumatran rhino, died at about 30 years old from what was believed to be old age (Sumatran rhinos live to their late 20s to mid-30s). Tam had lived at the same sanctuary as Iman in Borneo, though the two never successfully mated.

The remaining Sumatran rhinos in captivity are all in southeast Asia; the Cincinnati Zoo was the last U.S. facility to have a Sumatran rhino. Harapan, a male born at the zoo, was sent to the Sumatran Wildlife Sanctuary in Indonesia in 2015 so he could have a chance to breed.

Roth knows firsthand what it’s like to say goodbye to a Sumatran rhino you’ve cared for.

“They’re incredibly sweet. That really surprises people — they think of rhinos as these big powerful beasts,” she said. “They’re pretty solitary in the wild; if you capture them, they’ll be eating out of your hand in 24 hours.”

Susie Ellis, executive director of the Texas-based conservation nonprofit International Rhino Foundation, offered condolences to the Sabah government and the Borneo Rhino Alliance. She pointed to the possibility that Iman’s legacy might endure with the help of science: The Borneo Rhino Sanctuary previously harvested Iman’s egg cells with the hope of one day creating a viable Sumatran rhino embryo.

“There is limited knowledge about Sumatran rhino reproductive physiology, and converting cells in a laboratory into viable embryos is complex,” Ellis said. “Still, there is hope for the survival of Sumatran rhinos.”

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