Earlier this week, Nabiré, one of the last remaining northern white rhinoceroses in the world, died at the age of 31. According to a statement from Dvůr Králové Zoo in the Czech Republic, where Nabiré was born and spent her life, she died from “a large pathological cyst that ruptured inside her body.”

Since 1975, the Dvůr Králové Zoo has succeeded in breeding northern white rhinos, who are on the brink of extinction — only four remain across the globe, with none in the wild in their native Central Africa. Nabiré participated in the zoo’s breeding program, but couldn’t conceive because of cysts in her uterus. Her left ovary, however, was potentially healthy, so the zoo removed it immediately following her death, hopeful that her eggs can be used for artificial procreation.

None of the three surviving female northern white rhinos have successfully conceived. Nola, part of the original 1975 breeding group, now lives at the San Diego Zoo, where a rhino has never given birth. Nájin and Fatu — the other two, both born at Dvůr Králové Zoo and moved to Kenya in 2009 — have not conceived, so a team from the Leibniz Institute for Zoo and Wildlife Research in Berlin plans to harvest mature ovary cells for fertilization. Any successful embryos would be transferred to a surrogate mother of southern white rhino origin.

Přemysl Rabas, the zoo’s director, called Nabiré’s death “a terrible loss” and “a symbol of the catastrophic decline of rhinos due to a senseless human greed.” In the wild, the northern white rhinos have reached extinction, the zoo claims; therefore, the four remaining rhinos, as well as Nabiré’s eggs, remain the last hope for survival of the species.

Photos via Joel Sartore, Hynek Glos/ZOO Dvůr Králové