A southern white rhino named Victoria gave birth to a healthy male calf on July 28, according to San Diego Zoo Global, marking the first successful birth from artificial insemination of a southern white rhino in North America. The calf is reportedly nursing well, and is currently bonding with his mother in a quiet setting away from visitors.

Victoria is one of two southern white rhinos at San Diego Zoo Safari Park who were artificially inseminated in 2018, part of a long-term effort to save the northern white rhino from extinction. Although both mothers have been carrying southern white rhino babies, their pregnancies are part of a careful testing process for southern white rhinos to eventually serve as surrogate mothers of baby northern white rhinos. The other mother-to-be, Amani, is due in November or December.

Only two northern white rhinos, a distant subspecies, are alive; both are female but neither can bear a calf. The last male northern white rhino, named Sudan, was euthanized in March 2018 at a preserve in Kenya due to age-related health problems.

Researchers hope that one day Victoria and Amani could serve as surrogate mothers, giving birth to a northern white rhino baby. They're optimistic a northern white calf could be born this way within 10 to 15 years, and the work could also be applied to other rhino species, including critically endangered Sumatran and Javan rhinos.

Victoria and Amani are two of six female southern white rhinos relocated to the San Diego park from private reserves in South Africa. The San Diego Zoo Institute for Conservation Research is conducting tests on all of them to see if they would be successful as surrogate mothers.

Researchers point out the calf in Victoria's ultrasound.

Seven-year-old Victoria was the first to become pregnant in 2018, and 10-year-old Amani followed suit a few months later. Researchers have been watching them closely to see if they successfully carry their calves through the gestation period, which typically lasts 16 to 18 months.

"We are so pleased Victoria and the calf are doing well. She is very attentive to her baby, and the calf is up and walking, and nursing frequently," San Diego Zoo's Barbara Durrant said in a statement. "Not only are we thankful for a healthy calf, but this birth is significant, as it also represents a critical step in our effort to save the northern white rhino from the brink of extinction."

The zoo institute has the cells of 12 individual northern white rhinos stored at its "Frozen Zoo." Scientists hope to convert those preserved cells to stem cells, which could develop into sperm and eggs to be used to artificially inseminate the female southern white rhinos.

A breakthrough with embryos

Shortly after the announcement of Victoria's pregnancy, an international team of scientists announced the successful creation of embryos from the sperm of deceased northern white rhinos and the eggs of southern white rhinos. They used electrical pulses to stimulate the sperm and egg to fuse together. After this success, the hope is they can extract eggs from the last two surviving northern white rhinos — who are currently living in a Kenyan national park under 24-hour guard.

And in an encouraging test of that strategy, researchers announced in late June 2019 they had successfully transferred a test-tube embryo of a southern white rhino back into a female whose eggs were fertilized in vitro. The procedure took place at the Chorzow Zoo in Poland, the Associated Press reports, as part of the BioRescue research project aimed at saving the northern white rhino. This embryo is a southern white rhino, but it's a key step in testing the process that scientists hope will eventually yield a newborn northern white rhino.

Najin (left) and Fatu, the only two remaining northern white rhinos, graze together at Kenya's Ol Pejeta Conservancy in 2018.

"This is the first positive proof that the entire procedure we've developed in theory can be successful," professor Thomas Hildebrandt, from the Leibniz Institute for Zoo and Wildlife Research in Berlin, told the AP. Ultrasound tests show the embryo has grown, he added, although it's smaller than expected and has not yet implanted in the mother's uterine lining.

A study published in the Proceedings of The Royal Society B also offered hope that artificial insemination will be successful in the future. Researchers analyzed DNA from living southern white rhinos and compared it with DNA from museum specimens of northern white rhinos. They discovered the two subspecies are more closely related than previously thought and crossbred for thousands of years after the species split.

"Everyone believed there was no hope for this subspecies," Hildebrandt told BBC News. "But with our knowledge now, we are very confident that this will work with northern white rhino eggs and that we will be able to produce a viable population."

Editor's note: This article has been updated with new information since it was originally published in May 2018.