A northern white rhinoceros has died at the San Diego Zoo Safari Park, leaving just five of the animals in the world. The 44-year-old male rhino, named Angalifu, apparently died of old age Sunday, the Associated Press reports. Conservationists at the park had hoped that Angalifu would mate with a female northern white rhino named Nola, but their attempts proved unsuccessful.

"Angalifu's death is a tremendous loss to all of us," Randy Rieches, the safari park curator, said in a statement. "Not only because he was well beloved here at the park but also because his death brings this wonderful species one step closer to extinction."

In addition to Nola, there are three northern white rhinos at a preserve in Kenya and one at a zoo in the Czech Republic. Last week, authorities at the Kenya sanctuary announced that their one male and two females will not breed naturally, forcing them to try in-vitro fertilization instead.

There were around 2,000 living northern white rhinos as recently as 1960, mostly in southern and central Africa, but poachers soon ravaged the population. By 1984, there were just 15 remaining. Rhino horn is believed to hold healing powers in traditional Asian medicine, and high demand for the material has driven up prices on the black market. Earlier this year, officials in South Africa announced that more than 1,000 rhinos were killed in 2013, nearly double the previous year's total.

Although the outlook may seem grim for the northern white rhino, there is cause for hope. The southern white rhino was considered extinct in the 19th century, until a small population was discovered in South Africa. Ensuing conservation efforts gradually brought the animals back to life. According to WWF, there are more than 20,000 southern white rhinos alive today.