A census of the world's largest mountain gorilla population has counted 480 animals, an increase of 100 - more than a quarter - since the last count in 2003.

The gorillas surveyed live in Central Africa's Virunga Massif region, a volcanic mountain ecosystem consisting of three adjacent national parks spanning parts of Democratic Republic of the Congo (DRC), Uganda and Rwanda.

A fourth park, southwestern Uganda's Bwindi, is home to an additional 302 mountain gorillas, the only other remaining wild population, which together with four orphaned mountain gorillas in a sanctuary in the DRC brings the wild population to 786.