A joint survey by two conservation groups, World Conservation Union and the World Wildlife Fund, says the black rhino population has risen to over 3,600. That is an increase of 500 animals over the last two years.

A World Wildlife official, Taye Teferi, says the biggest challenge facing the species is making sure current conservation efforts are maintained.

Conservationists say the black rhinoceros had been on the decline since the 1970s, when their numbers dropped from 65,000 to only 2,400 in the mid 1990s.

They say the single most important cause for that decline has been the demand for their horns in the Middle East and East Asia.