A BBC team films two troops, a few dozen each, of the rare mountain gorillas, of whom less then 800 are estimated to remain in the wild. Although their biotope has shrunk to a relatively small area around the Great lakes, conditions are quite different in Rwanda's volcanic mountain jungle from Uganda's bamboo-grown hills forest. Life is hard because of dwindling territory, poaching, human infectious diseases and family dramas. Silverbacks (ripe males) either leave the troop to seek their own harem or stay and challenge the patriarch. The young need five years of intensive parenting, sometimes falling to the father after the mother is lost.