With the death of a 44-year-old male named Angalifu, there are only five northern white rhinos left in the world, according to the San Diego Zoo Safari Park, which tweeted the news along with the above photo on Sunday. He came to California from the Khartoum Zoo in Sudan in August 1990, U-T San Diego reports. He died of old age.

"Angalifu's death is a tremendous loss to all of us," park curator Randy Rieches said in a statement to AP. "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."

The northern white rhinoceros (Ceratotherium simum cottoni), also known as the square-lipped rhino, once lived throughout parts of Uganda, Chad, Sudan, Central African Republic, and Democratic Republic of the Congo. As the second largest land animal, they can reach nearly two meters (six feet) in height, and the males can weigh up to 3,600 kilograms (almost 8,000 pounds). But their horns are valued for dagger handles and as aphrodisiacs, and poaching gangs have obliterated the species in the last five or so decades.

The remaining five are found at the San Diego Zoo (a female named Nola), Dvur Kralove Zoo in the Czech Republic, and three in a preserve in Kenya, Washington Post reports. The three in Kenya -- a male named Sudan and two females named Najin and Fatu -- were sent to Kenya in hopes that they’d breed in a more natural setting.

Attempts to mate Angalifu with Nola have been unsuccessful, and just last week, preservationists at the Ol Pejeta Conservancy in Kenya said that their one male and two females will not reproduce naturally. "Gauging the estrus cycle of the female is difficult,” Rieches tells the Los Angeles Times. "The rhino is one of the species that we're still working on to perfect artificial insemination." In vitro fertilization might be the only hope to keep the species alive.

Sizeable populations of the southern white rhinoceros (C. s. simum), a conservation success story, can be found in South Africa, with smaller reintroduced populations living throughout the southern half of the continent. One of these females may become a surrogate mother for the northern subspecies.