After this weekend, only three northern white rhinos are left in the world

One of the world’s last four remaining northern white rhinoceroses died this weekend, leaving big questions about the future of the species.

Until this weekend, San Diego Zoo’s 41-year-old Nola was the only female northern white rhino in the Western hemisphere. But after she underwent surgery on Nov. 13, her health deteriorated rapidly.

Today, Nov. 23, the zoo announced on Facebook that it had put Nola down, asking followers to share the hashtag #Nola4Ever in her honor.

Three northern white rhinos remain at the Ol Pejeta Conservancy in central Kenya. One, named Sudan, is the only northern white male in the world capable of breeding, but has “disappointingly low” sperm count according to Ol Pejeta’s website. Neither of the two females are capable of natural reproduction.

Earlier this month, before Nola’s surgery, the San Diego Zoo brought in six southern white rhinos—a more plentiful subspecies—to serve as surrogates for northern white rhino embryos. However, scientists have yet to prove that the two subspecies are genetically similar enough to reproduce, according to the BBC.

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