Five of the world's most critically endangered animals spent their first day in a new home over the weekend after the start of the "most ambitious" international relocation of its kind.
Three female and two male eastern black rhinoceroses were airlifted from a South African conservancy to Tanzania's Serengeti National Reserve.
They were the first of 32 of the animals that will be flown to the native habitat from which their ancestors were evacuated almost 50 years ago.
The trade in rhino horn in the 1960s and 1970s pushed the rare species -- one of 188 mammals on the international "Red List"' of critically endangered animals -- to the brink of extinction.
From a peak population of more than 1,000 in the Serengeti area in the middle of the last century, only two females remained by 1991. However, in 1964 conservationists moved seven of them to South Africa, where they thrived in private game parks.
Now, they are returning home for the first time.
All 32 to be sent to Tanzania over the next two years of the Serengeti Rhino Repatriation Project are direct descendants of the seven evacuated 46 years ago.
"It is the largest amount of such animals ever to be moved so far," said Alistair Nelson, program manager for the Frankfurt Zoological Society, which oversaw the relocation.
The operation began six weeks ago, when Piet Morkel, with long experience of using tranquilizer darts on the animals, captured the first of the 32 in their South African conservancy. Since then, they have been kept in large, specially constructed pens.
Two handlers stayed with them to help familiarize them with enclosed spaces, steadily introducing them to the crates used during the flight.
Early on Friday, each of the 1.2-tonne animals was loaded onto the Hercules for the five-hour, 3,000-kilometre journey.
The plane was met by Tanzania's president, Jakaya Kikwete, at a welcome ceremony involving 500 people.
"This is a historic day -- we are welcoming home these animals in the first ever relocation of its kind in the world," said Simon Mduma, director of the Tanzanian Wildlife Research Institute.
Conservationists estimate there are fewer than 4,300 black rhinos left in the wild, down from a peak of 65,000 in the middle of the 20th century. Only 33 live in the Serengeti ecosystem.
The five that arrived on Friday will spend a month in a new set of pens before being released into a 40-square-kilometre enclosure ringed with an electric fence. Only after they are fully acclimatized will they be introduced fully into the wild. "That's going to take about a year," said Brian Harris, managing director of the SingitaGrumeti Fund, a private conservation foundation.
Poaching driven by increased Chinese demand has soared in east Africa in the past five years. Six black rhinos were killed for their horns in neighbouring Kenya in the last 12 months, and measures have been put in place to protect the new arrivals.
An elite force of 24 rangers has been specially trained to monitor the rhinos, which will have GPS chips inserted in the horn.
Harris said the ultimate aim was to rebuild the biodiversity of the Serengeti ecosystem. "Reintroducing the rhinos and ensuring their safety from poachers will automatically protect other species sharing the same habitat," he added.
