A rare black rhino has died while on a 5,000-mile flight from Kent to Africa, where he was due to be released in the wild.

Zambezi, a 17-year-old male, was born and raised in animal reserves controlled by the Aspinall Foundation but was on his way to Tanzania as part of ongoing conservation efforts to boost the critically endangered population when he died.

Zambezi was under the care of the Aspinall Foundation, which owns nature reserves in the UK. He was also accompanied by a team from the Grumeti Fund Reserve where he was set to be released, African keepers and a veterinarian experienced in the movement of large animals.

“We do not yet know what caused his death,” said Damian Aspinall, the chairman of the foundation, who said he was “shocked and devastated by the loss”.

He announced an inquiry into Zambezi’s death “to see if there are lessons to be learned”.

Conservation success for the Gorongosa National Park in Mozambique Show all 8 1 /8 Conservation success for the Gorongosa National Park in Mozambique Conservation success for the Gorongosa National Park in Mozambique Tourists observe elephants Left devastated by Mozambique's civil war, Gorongosa National Park is now thriving Bob Poole / Gorongosa National Park Conservation success for the Gorongosa National Park in Mozambique Waterbuck graze in the open floodplains A restoration project with government backing has battled poachers who were depleting the already slim animal populations AFP/Getty Conservation success for the Gorongosa National Park in Mozambique Hippos take a dip In 2008, there were around 10,000 large animals in Gorongosa; today there are over 100,000 J Da Silva / Gorongosa National Park Conservation success for the Gorongosa National Park in Mozambique Wild dogs in Gorongosa National Park Tourism is an important part of the restoration project Gorongosa National Park Conservation success for the Gorongosa National Park in Mozambique Waterbuck on the savannah Tourists create jobs for locals, expanding the conservation workforce, and safaris in Gorongosa are used to educate visitors about the project Getty Conservation success for the Gorongosa National Park in Mozambique A lioness The civil war killed 95% of Gorongosa's lion population, today there are 104 lions who are monitored by conservationists Ticky Rosa / Gorongosa National Park Conservation success for the Gorongosa National Park in Mozambique Sunset over the Gorongosa National Park Sunset over the National Park Gorongosa in the center of Mozambique. istock Getty Conservation success for the Gorongosa National Park in Mozambique Tourists in Gorongosa National Park Tourists in Gorongosa National Park Credit: Bob Poole / Gorongosa National Park Bob Poole / Gorongosa National Park

The foundation defended its decision to transfer the animal from its Port Lympne Reserve in Kent, saying the practice of relocating black rhinos born in captivity to Africa is safe and increasingly common.

“The Aspinall Foundation has previously successfully returned eight black rhinos to their native homelands,” Mr Aspinall said. “In other worldwide organisations, 19 black rhinos have been successfully relocated.”

Black rhinos are listed as “critically endangered” by the World Wide Fund for Nature (WWF).

Their population declined dramatically in the 20th century at the hands of European hunters and settlers.

According to the WWF, black rhinos came close to extinction after their numbers dropped by 98 per cent between 1960 and 1995.

Their numbers have rebounded to between 5,000 and 5,500 but they are still threatened by loss of habitat and poaching – rhino horns are sold at exorbitant prices in China and Vietnam, where they are used for traditional remedies.

Black rhinos are smaller than their white counterparts and can be distinguished by their pointed – rather than square – lip.

The Aspinall Foundation had announced its decision to move Zambezi on 26 June and chronicled his journey on Facebook.

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After the animal’s death, Mr Aspinall said that the foundation will continue to seek to return endangered species to protected areas in the wild.