NAIROBI, Kenya — The death of the world's last male northern white rhino, Sudan, doesn't end efforts to save a subspecies of one of the world's most recognizable animals. The focus now turns to his stored semen and that of a four other dead rhinos, as well as the perfection of in vitro fertilization techniques and the critical need to keep the remaining two females alive.
Whatever happens, conservationists hope the lessons learned in the endeavor can be applied to other critically endangered species.
The 45-year-old Sudan, who won widespread affection last year with his listing as "The Most Eligible Bachelor in the World" on the Tinder dating app in a fundraising effort, was euthanized on Monday after "age-related complications," researchers said Tuesday.
In his death, the world saw the shadow of extinction approach before their eyes. "Utter tragedy today," British Foreign Secretary Boris Johnson tweeted. "We can't just sit back and watch more species disappear."
The rhino "stole the heart of many with his dignity and strength," said the Ol Pejeta Conservancy in Kenya, where Sudan lived. It said his condition had "worsened significantly," to the point where he was no longer able to stand. His muscles and bones had degenerated and his skin had extensive wounds, including a deep infection on his back right leg.
Euthanasia was "the best option, given the quality of his life had deteriorated to a point where it was unfair to him," chief conservation officer Samuel Mutisya told The Associated Press.
Sudan had been central to the ambitious effort to save the subspecies from extinction after decades of decimation by poachers, along with the two surviving females. One is his 27-year-old offspring, Najin, and the other is her 17-year-old offspring, Fatu.
It is now just a matter of months before eggs are extracted from the two females, said Jan Stejskal, director of international projects at Dvur Kralove Zoo in the Czech Republic, where Sudan lived before coming to Kenya.
Scientists have developed a technique to extract the eggs, using females from the similar southern white rhino subspecies from European zoos, Stejskal said. The genetic material would have to be transferred to a lab in Italy that he said was the only place where embryos of northern white rhinos can be created.
Creating embryos has been tried only on southern white rhinos and it isn't guaranteed the procedure will work on northern white rhinos, Stejskal added.
"It would be a miracle to succeed on the first try," he said. "Chances are we won't succeed and will have to travel to Africa for the eggs in several months again."
If the procedure is eventually successful, scientists will use southern white rhinos in Kenya and in European zoos as surrogate mothers.
While chances of success with in vitro fertilization are slim "we believe that giving up is not an option," the veterinarian at the Kenya conservancy, Dr. Stephen Ngulu, told the AP.
Teams in Europe and the United States also have been working for years on the possibility of using stem cell technologies to create an embryo, but that route would take years longer.
Sudan ended up being part of that work as well. "His genetic material was collected yesterday and provides a hope for future attempts at reproduction of northern white rhinos through advanced cellular technologies," the Kenya conservancy said.
The ultimate goal is to create a herd of five to 15 animals that would be returned to their natural habitat in Africa. That could take decades.
Sudan's death "is a cruel symbol of human disregard for nature and it saddened everyone who knew him. But we should not give up," Stejskal said. "It may sound unbelievable, but thanks to the newly developed techniques even Sudan could still have another offspring."
Sudan was the last of his kind to be born in the wild, in the country that is his namesake. He was taken to the Czech zoo and then transferred to Kenya in 2009, along with the only other remaining northern white rhinos, the two females and a male who died in 2014.
They were placed under 24-hour armed guard and fed a special diet. "However, despite the fact that they were seen mating, there were no successful pregnancies," the conservancy said.
Rangers caring for Sudan described him as gentle and, as his condition worsened in recent weeks, expressed sadness over his imminent death.
Some groups, including London-based Save the Rhino, have said in vitro fertilization is probably too late to save the northern white rhino, whose natural habitat in Chad, Sudan, Uganda, Congo and Central African Republic has been ravaged by conflicts in the region. They say the efforts should focus on other critically endangered species with a better chance at survival.
Other rhinos, the southern white rhino and another species, the black rhino, are under heavy pressure from poachers who kill them for their horns to supply illegal markets in parts of Asia.
Roughly 20,000 southern white rhinos remain in Africa.
Associated Press writers Karel Janicek in Prague, Czech Republic, and Christopher Torchia and videographer Josphat Kasire in Nairobi, Kenya, contributed to this report.