The gorillas are found only in the dense forests straddling the border between Rwanda, Uganda and eastern Congo. With fewer than 750 left, they are one of world's most endangered species.

The UWA has habituated four social groups of six to seven gorillas each in Uganda's Bwindi Impenetrable Forest, meaning they are accustomed to seeing people and do not lash out or run away.

Rangers and primatologists accustom the gorillas by spending progressively more time close to them each day.

"We plan to start habituating two more groups (in Bwindi) soon, but it will probably take two years before they will be ready to take visits from tourists," said Sam Mwanda, UWA deputy director. Another reserve has one habituated group.

The UWA says each group can only receive eight tourists per day -- any more stresses them out and puts them at greater risk of catching potentially lethal diseases.

In July, the government put up the price of a gorilla visiting permit to US$500 per day, but waiting lists have persisted.

"Habituating these groups will increase tourist revenue. We will use this money for conservation in community projects and better enforcement," Mwanda said.

Mwanda said tourist dollars had funded conservation efforts boosting the region's gorilla population from 650 in the mid-1990s to 750 -- a rare recovery for a species with so few individuals left.

Tourism and coffee are Uganda's top earners.