Nola weighed in at a whopping 4,500 pounds (2042 kg); white rhinos are the heaviest rhinos, weighing more than all other land mammals except elephants.
The zoo's veterinarians attempted to operate on Nola on November 13, but to no avail: a few days after the surgery, her health worsened. She lost her appetite and became listless, and the vets decided to put her out of her misery on Sunday.
“Nola was an iconic animal, not only at the San Diego Zoo Safari Park, but worldwide,” a park statement read.
The remaining three northern white rhinos have been settled in a closely-guarded park in Kenya. After Nola’s death, the San Diego Zoo Safari Park purchased six young South African female southern white rhinos in order to preserve the species.
The Safari Park has developed a genetic cryostorage project, the "Frozen Zoo", in collaboration with the Scripps Research Institute in La Jolla, California to help save endangered species. The zoo hopes to use the viable stem cells it has taken from twelve white rhinos since 1979 to restore genetic variation. The zoo workers hope to develop embryos to implant in the six new rhinos, so they may one day serve as surrogate mothers for a resurrected generation of northern white rhinos, born in captivity.
San Diego scientists estimate that this may take about 15 years.
According to the World Wildlife Foundation, there are 20,000 southern white rhinos; northern white rhinos and southern white rhinos are genetically distinct subspecies which inhabited different regions in Africa. In 1895, less than 100 southern white rhinos were left after poachers had nearly eliminated the population. However, today the endangered animals remain threatened.
While poachers sought ivory in the 19th century for the production of artwork, pianos and billiard balls, 21st century demand for rhino horn originates in Vietnam. Rhino horn is prized among wealthier Vietnamese, as according to traditional medical beliefs it is capable of treating cancer and other diseases. According to The Atlantic, "the country's appetite for rhino horn is so great that it now fetches up to $100,000/kg, making it worth more than its weight in gold."
Another northern white rhino, Angalifu from Sudan, died at the San Diego Zoo of old age several days short of his 44 birthday in December, 2014.
Previously, researchers had hoped to save the endangered northern white rhinos by artificially inseminating females.