Rangers protecting the endangered blacks rhinos of East Africa have taken to the trees.
In the 1980s, an uncontrolled poaching spree reduced the rhino population by 98%, but anti-poaching activities have now given the rhinos a chance to recover their numbers and rebuild populations.
Patrols mean black rhinos may flourish from now on
However, the problem of accurately monitoring the rhinos to implement realistic wildlife management strategies remains.
Although the collective noun for rhinos is "crash", in practice they are fairly solitary.
Difficult to track
Friedrich Alpers, the project co-ordinator of the Selous Rhino Trust team in southern Tanzania, searches not only for the elusive rhinos, but also strategically positioned trees.
As the rhinos' favourite habitat in Tanzania's Selous is thick bush, unconventional techniques must be used.
Mr Alpers, a Namibian rhino expert, now spends up to seven days in a single tree to get sightings of the shy rhinos.
Rhinos are hunted for their horns
"As rhinos have weak eyesight, they would not spot me, but the real challenge would be to bypass their acute sense of smell. So I solved this problem by rubbing fresh elephant dung on my body and daily refreshed this fragrance."
On his first tree stake out, Mr Alpers found the elephant dung did not fool a sharp-sighted leopard who stalked him for several hours but was unable to reach his living area of suspended fishing nets.
After several nights of listening to a pride of lions ambushing antelopes and feeding below him, he sighted a rhino, known to the Selous team as Mary.
With her was a calf called Audax, named after the ranger who identified the tracks.
On his recent stint in a big tamarind tree near a waterhole, Mr Alpers blended into his surroundings of foliage and branches.
"This was tested to perfection when the local troop of baboons - later to become my allies in leopard detection - came to visit and drink without noticing me.
"It was a privilege to see unstaged animal behaviour; I felt like part of the system."
After four days of eating only nuts, dried vegetables and biltong, he spotted his rhino.
"He was a beautiful mature 25-year-old male. He approached slowly, ever so cautiously as he is the dominant male of this area.
"I was clinging to my tree in disbelief, but he wasn't aware of my disguised presence."
After a drink at the waterhole, the male rhino disappeared into the night.
From an estimated 3,000 rhinos in the 1960s before the poaching, there are now believed to be at least 20 black rhinos in the Selous in Tanzania, enough to form a viable breeding population.
In the whole of East Africa the population has risen to 504 animals.
Poaching is still a problem, with most of the rhino horn from East Africa being smuggled to the Yemen where it is made into ornamental dagger handles.
But the anti-poaching measures, from patrols to paying rewards to informers, may mean the black rhinos have a real chance to flourish once again.