Moving endangered rhinos to new areas is a vital part of their conservation. War-torn helicopters from the Vietnam war are airlifting the creatures to safety.

Zipping through the skies over South Africa, a 1,300kg (2,865lbs) horned herbivore is dangling by its feet from a helicopter. It may be a shocking sight to behold but, within the last decade, the use of helicopters in rhinoceros conservation has been gaining momentum in South Africa, Namibia and Botswana.

Black rhinos are critically endangered, according to the International Union for Conservation of Nature (IUCN). However, thanks to conservation efforts, their numbers are on the rise. Today, black rhinos have a population of roughly 6,500 – up from the 1990s' low point of less than 2,500, when poaching and habitat loss drove the species to the edge of extinction.

Black rhinos are moved around for three reasons, says Ursina Rusch, population manager for the WWF South Africa Black Rhino Range Expansion Project. First, to protect them from poaching. Secondly, for monitoring purposes – rhino researchers often take the opportunity to insert satellite GPS telemetry into the rhinos' horns. And, thirdly, to ensure their genetic population is as diverse as possible. The species mostly exists within protected pockets on public and private reserves, so translocation is one of the only available methods to increase their range.

"If we don't translocate rhinos and create new populations, they will inbreed enough that they crash, or run out of resources and stop breeding," says Rusch. Black rhino population growth rates are density dependent. This means if a rhino community is too crowded, the females will start having longer intercalving periods – the time between the birth of one calf and the next – and so produce fewer calves, an evolutionary response and adaptation to resource management.

While the transport of animals for population regrowth and genetic diversity isn't new, the regular use of helicopters in this fight is. Beginning in the 1990s but refining methods since the 2010s, helicopters have "revolutionised the world of rhino conservation", says Rusch. Her WWF project has translocated around 270 rhinos, of which about 160 have been airlifted.

Leaning from an airborne helicopter, a veterinarian "darts the rhino in the bum" with immobilising drugs, typically targeting youngsters or dominant bulls that need to be removed to prevent inbreeding, says Rusch. Rhino immobilisation typically involves a potent opioid and a tranquilliser.

Whereas before veterinarians would have spent 20 minutes on-foot tracking a half-way-sedated rhino, the helicopter team now saves precious time by aerially tracking the rhino – and within four minutes, the rhino falls unconscious, says Rusch. By the time the rhino goes down, the ground team and the helicopter team spring into action: quickly approaching the rhino for processing. They take biological samples and measurements and insert microchips for monitoring.

Next, the crew ties big, soft straps around the rhino's four ankles. The straps connect to a single rope which is hooked to the underside of the helicopter.

Then the move happens. The helicopter airlifts the rhino, which dangles below, to a central location – generally an open field – where ground crews are waiting, says Rusch.

Historically, the rhino would have been woken up from the immobilising drug and walked into a crate, before being hoisted onto the........

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