No white rhinos are known to remain in the wild, and the animals transported on Sunday have produced no offspring after nearly 24 years in a Czech zoo. So wildlife workers hoping to save the subspecies loaded two males and two females into wooden crates and began the effort to return them to what was once their savannah homeland.
When teams of Kenyan wildlife workers opened the crates on Sunday, two of the rhinos lingered several minutes before moving to a larger pen as Czech animals handlers coaxed them out with soothing words and treats. The other two exited immediately.
The rhinos' handlers and park officials said they hoped the two females will bear as many young as possible for several years, but all those involved acknowledged it was not a sure bet that the rhinos would reproduce.
The northern white rhino is the world's rarest large mammal, making the international effort to save the subspecies all the more important.
"Objective No. 1 is to get as many offspring as you can from the females - at least one calf out of each within two years," said Rob Brett, the director of Fauna and Flora International, which helped arrange and finance the move.
The rhinos were transported in large wooden crates by the international shipping company DHL on two flatbed trucks. On the side of the crates was written: "Last Chance to Survive."
The four were flown from a zoo in the Czech Republic to the Ol Pejeta Conservancy - about 180 miles (300 kilometers) north of the capital, Kenya - where a black rhino population has made strong gains and the rhinos will be protected from poachers.
The rhinos have not reproduced in the Czech Republic since 1985, the reason for the move to Kenya. Two northern whites remain behind; two others are in San Diego. The females could be mated with southern white rhinos - a different subspecies - to keep the gene pool alive.
The aim of the project - years down the line - is to reintroduce the northern white rhino back to southern Sudan, the Democratic Republic of Congo and Cameroon, said Patrick Omondi, head of species conservation and management for the Kenya Wildlife Service.
Alastair Lucas, the vice chairman of Goldman Sachs in Australia, helped finance the rhinos' move to Kenya, a project he became involved with earlier this year after visiting Uganda and being told parks there no longer have rhinos. He declined to say how much he donated or the cost of moving the animals.
"Shipping rhinos across the world is not cheap. They don't fit in economy seats," Lucas said. "I had to fly them business class."
The rhinos will remain penned in the Kenyan park as they acclimate to the climate and vegetation. They will be given more room to roam in coming weeks and eventually released to the entire park.