Five critically endangered eastern black rhinos from wildlife parks in three European countries are ready to be transported back to their natural habitat in Rwanda, where the entire rhino population was wiped out during the Rwanda Civil War in the 1990s.

Officials from the Czech Republic's Dvur Kralove zoo said Thursday that the three female and two male rhinos have been slowly trained to get used to custom-made transport boxes to take them to Akagera National Park in eastern Rwanda, which is now considered safe for rhinos.

Their journey will mark the biggest single transport of rhinos from Europe to Africa. Transporting them won't be easy and the animals will have to be tranquilized several times during the trip. The rhinos weigh between 850 and 1,150 kilograms.

The rhinos first met in November when the three already at the Dvur Kralove zoo were joined by one from Flamingo Land in Britain and one from Ree Park Safari in Denmark.

"Even though they have been well prepared, you know it is still a long trip, it is stressful, it is stressful for me, it is probably stressful for them," said Pete Morkel, an internationally recognized veterinarian from Zimbabwe and expert on rhino relocation.

"It is not easy moving black rhino, they are explosive animals, and they can get unhappy very quickly. So you have to keep your finger on the pulse and see what happens and respond accordingly," Morkel said.

When they get to Rwanda, the rhinos will undergo a lengthy process of adaption before they will be allowed to roam freely and join 18 eastern black rhinos that were transported to the park from South Africa in 2017.

More than 500,000 people were killed in the Civil War in Rwanda. The conflict also devastated the entire population of lions there.

Rwanda's ambassador to Berlin, Igor Cesar, described the transport as "historic" and recognition for his country's efforts to restore its wildlife diversity.

African rhinos remain under intense pressure from poachers who kill them to meet demand for their horns in illegal markets. There are only a few hundred of the eastern black subspecies remaining in the world.

Listed as Critically Endangered by the IUCN Red List of Threatened Species, the eastern black rhino is a subspecies of the black rhinos, and had a historical distribution from South Sudan, Uganda, Ethiopia, down through Kenya into north-central Tanzania. Today, its range is limited primarily to Kenya, Tanzania, and Rwanda.

(Cover image shows black Rhinos Mandela and Jasiri at Safari Park Dvur Kralov, in Dvur Kralove nad Labem, Czech Republic. /AP Photo)

(If you want to contribute and have specific expertise, please contact us at nature@cgtn.com.)