In 2009 four of the world's last seven northern white rhinos (Ceratotherium simum cottoni) were moved from a zoo in the Czech Republic to Ol Pejeta Conservancy in Kenya. At the time conservationists expressed hope that returning the rhinos to semi-wild lives under their native African skies would help inspire the animals to mate and, if they were extremely lucky, save the species from extinction.

No such luck. There were a few half-hearted couplings in early 2011, neither of which resulted in pregnancies, but for the most part, the rhinos showed little to no interest in breeding. Maybe they had spent too much time in captivity. Maybe they were getting old. Maybe they just sensed that they were the last of their kind and wanted to go quietly into the night.

But now something incredible has happened. Not only have two rhinos suddenly started expressing interest in each other, they have actually gone ahead and mated. Ol Pejeta Conservancy posted this bow-chicka-wow-wow video on April 30:

How did this happy event come to pass? Let's go back a few months: The four northern whites had been kept in two different enclosures, with one male and one female in each. Rhinos named Najin and Suni lived by themselves in one 40-hectare enclosure (called a boma). Sudan and Fatu lived in a much larger boma (242 hectares) accompanied by six southern white rhinos, two black rhinos and quite a few other critters. Caretakers included the southern whites (C. s. simum) in the hope that the northern rhinos would breed with them and pass their genetic material to future generations in hybrid offspring. (In fact, one of the unsuccessful matings in 2011 was between a northern and southern white.) In January the committee responsible for the northern white rhinos' care decided to mix things up and switch the pairs into each others' bomas to see if their behavior would change in slightly different habitats.

But before they did that, the team wanted to add two female southern whites into the enclosure containing Najin and Suni, a move intended to acclimate them to presence of other rhinos. The first southern white rhino moved into the enclosure February 23, followed by a second March 8.

The addition of the two new rhinos to the boma, however, had an unexpected effect: Najin and Suni suddenly started acting...differently. As the conservancy posted on its web page: "On Friday March 27th, just two weeks after their new companions arrived, Najin and Suni became really interested in each other. The courtship ritual involved Suni smelling Najin's rump to determine her pheromone levels, and both of them grunting and chasing each other around. This lasted close to 12 hours—and we even caught it on video!"

What caused the pair's sudden mood change? The conservancy speculated: "Could the introduction of two extra females have excited Suni and made him want to mate? Or could the presence of other females have regulated Najin's cycling period? Whatever the case, we're happy our northern white rhinos are in the mating mood!"

It's too early to know if this rare and important mating has resulted in a pregnancy, but remain hopeful with fingers crossed for the future of this critically endangered species.

Photo: Two northern white rhinoceroses mating. Screen grab from video posted by Ol Pejeta Conservancy