Prince Harry is the new president of a conservation group called African Parks, which takes over national parks and gives rangers military-style training to take on poachers and protect wildlife. The BBC visited one of the parks it manages, at Zakouma in Chad.

A distant, guttural growl of elephants, and the occasional trumpet, drifted over the thick screen of lush trees and dry-scrub grass. The nearest calls were nearby, the furthest a mile or more away: this was the large herd we had been looking for.

Tracking collars had pinpointed them at dawn, but these elephants move quickly, and after centuries of hunting, run if they see, or even smell, humans.

The well armed rangers from the Mamba Two fast-response team fanned out ahead to the left and the right, not wanting to surprise, or be surprised by, a lone animal. They excitedly beckoned us to follow them slowly and carefully into a thicker section of trees.

It had been a three-hour flight in a small plane, from Chad's capital, N'Djamena, to Zakouma National Park, and a three-hour drive to this section in search of the herd, the last of the park's elephants.

Tens of thousands once lived in this reserve covering 3,800 sq km (1,470 sq miles), but for centuries it was the nearest place Sudanese horsemen could find ivory, much coveted by Arab traders along the Nile. 

Originally they hunted with spears and swords, but modern AK47 assault rifles allowed killing on an industrial scale. 

Janjaweed mercenaries from Dafur, in western Sudan, continue to be the biggest poaching threat, with heavily armed, military-trained raiding parties on horseback targeting the elephant herds for their tusks. 

Zakouma has lost 90% of the 22,000 elephants it had in the mid-1970s.

• Chad country profile
• In pictures: The effect of Janjaweed attacks in Chad
• How the British Army is tackling elephant poaching
• US to lift ban on elephant hunting trophy imports

War with Libya and the upsurge in demand for ivory reduced the population to 4,300 by the early 2000s, and the chaos of civil war cut that to less than 500 by 2010.

Rangers were being killed, animals massacred in large groups, and it looked as if Zakouma's elephants were heading towards extinction. 

But in the past few years, an amazing transformation has taken place. 

In less than a decade a private, non-profit organisation has turned its fortunes around. 

African Parks manages some of the toughest to protect parks on the continent, and in Zakouma, at least, it has made incredible progress.

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