Céline Genton, a study author and conservation biologist at France’s University of Rennes, observed with her team the effects of Ebola on the gorillas’ survival rates and social dynamics from afar, from a platform in a jungle clearing using binoculars, a video camera, and powerful spotting scopes. Individual gorillas were identified by face shape, body shape, and pelage coloration. A control group—a population of gorillas unaffected by Ebola, separated by a river and 20 kilometers—was also observed.

During the outbreak, adult survival and reproductive potential were lowered among the gorillas, with the number of breeders immigrating into the population cut down by 50 percent. However, immediately after the outbreak subsided, the probability that the gorillas would form new breeding groups in the short-term rapidly increased again. Six years later, it had almost returned to normal. Likewise, adult gorillas’ survival rates returned to pre-epidemic numbers, highlighting “a certain resilience to rapid changes in the environment,” according to the study.