A grueling survey of vast tracts of forest and swamp in the northern Congo Republic has revealed the presence of more than 125,000 western lowland gorillas, a rare example of abundance in a world of rapidly vanishing primate populations.

As recently as last year, this subspecies of the world's largest primate was listed as critically endangered by international wildlife organizations because known populations - estimated at less than 100,000 in the 1980s - had been devastated by hunting and outbreaks of Ebola virus. The three other subspecies are critically endangered or endangered.