The species was down to its last six members last fall. Then there were five. Now, with the death of a northern white rhino in a Czech zoo, there are just four of the animals left in a species already past the point of no return.

Nabire, a 31-year-old female, died Monday in the same zoo where she was born; she was unable to produce offspring because she suffered from uterine cysts, one of which ended up killing her, Live Science reports.

"The pathological cyst inside the body of Nabire was huge. There was no way to treat it," said the zoo's rhino curator in a statement.

"Her death is a symbol of the catastrophic decline of rhinos due to a senseless human greed," the zoo's director said, per AFP. "Her species is on the very brink of extinction." With the death of Nabire, the only remaining northern white rhinos are three females who are unable to breed—an elderly female at the San Diego Zoo and two in Kenya—and the last surviving male, who's also at the Kenyan conservancy, where a last-ditch breeding effort to save the species failed, the AP reports.

In a Facebook post, the San Diego Zoo offered its condolences to the Czech zoo and said that instead of giving up on the species, it's collecting genetic material so the rhino's genome can be preserved.

The Czech zoo removed Nabire's healthy left ovary after her death, and the zoo's statement notes that the ultimate goal would be to generate northern white rhino embryos and transfer them into a closely related surrogate: the southern white rhino.

But scientists have not yet developed IVF procedures that work for rhinos, Live Science notes. (A cougar has come off the endangered species list—for a very bad reason.)

This article originally appeared on Newser: New Death Brings Rhino Species Down to Final 4

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