Poaching has pushed the rhinos to the brink of extinction, and attempts to breed them have been unsuccessful.
Angalifu was transferred to the San Diego Zoo in the late 1980s from a zoo in Khartoum, Sudan.
Attempts at captive breeding at the San Diego Zoo Safari Park have not been successful. Angalifu and Nola were unable to breed.
Just last week, preservationists at the Old Pejeta animal sanctuary in Kenya conceded that their one male and two female northern white rhinos will not reproduce naturally. The animals were flown from the Czech zoo to the Kenyan conservancy in December 2009 in hopes the natural environment could be easier for them to breed there than in captivity.
Efforts will now be made to keep the species alive through in vitro fertilization. That experiment could take place with a southern white rhino surrogate mother. Southern white rhinos almost went extinct at the end of the 19th Century, plunging down to only 20 at one point. Decades of conservation efforts gradually brought back their numbers