A census of mountain gorillas due in March will likely show numbers have risen this decade, experts said during a ceremony to mark Rwanda's expansion of its Volcano National Park.

The last global survey in the Democratic Republic of Congo, Uganda and Rwanda in 2010 found just 480 individuals of the critically endangered sub-species.

Eugene Mutangana, the head of conservation at the Rwandan Development Board (RDB), said an average of 18 baby mountain gorillas had been born each year in Rwanda since 2005, when the East African nation began naming them in an annual ceremony.