A Northern white rhinoceros, one of just four left on earth, has died at the San Diego Zoo Safari Park after suffering from a bacterial infection and age-related health issues, zoo officials said. Nola, a 41-year-old rhino brought to the Southern California park in 1989 as part of a breeding programme, took a turn for the worse over the weekend after a surgical procedure to drain a large pelvic abscess.The 1800kg rhino had been under watch as her appetite and activity levels declined."Nola was an iconic animal, not only at the San Diego Zoo Safari Park, but worldwide," the zoo said. "Millions of people learned about Nola and the plight of rhinos in the wild."Her gentle disposition and affinity for having her back scratched made her a favourite of the zoo's staff.Northern white rhinos were declared extinct in the wild in 2008 because of poaching for their horns, which are prized on the black market.Nola was the only member of her kind left in captivity in the western hemisphere. With her death, just three others remain, all at the Ol Pejeta Conservancy in Kenya, zoo officials said.Nola was born in the wild in Sudan and captured at about two years old. She arrived in California from a Czech zoo.Her death came weeks after six southern white rhinos were brought to San Diego from South Africa in an effort to bring Nola's kind back from the brink of extinction.Scientists are unsure if northern and southern white rhinos are two distinct species or subspecies of each other.Studies are under way to determine if southern whites, of which fewer than 20000 remain in the wild, are genetically similar enough to serve as surrogates for implanted embryos developed from northern white rhino DNA, zoo spokesman Christina Simmons said...