Mountain gorillas Gorilla beringei beringei are Critically Endangered, with just two small populations: in Bwindi Impenetrable National Park in south-western Uganda and the nearby Virunga Volcanoes on the borders with Rwanda and Uganda. A survey of the Bwindi population was carried out in 2002 and results were compared with the previous census in 1997. Our estimate of total population size increased over that period by c. 7% to 320 individuals and the structure and distribution of the population were largely unchanged. Signs of human disturbance were more common in 2002 than 1997, and gorillas tended to be found in areas of relative low disturbance. This suggested that disturbance could be a constraint on population growth and distribution but demographic stochasticity may also be responsible for the observed level of population change over a short time period. Other potential limiting factors, including habitat availability and disease, are discussed. While conservation activities in Bwindi have probably contributed to the stability of the population, strengthening of law enforcement and continued vigilance are needed to ensure the population's long-term growth and survival.

Mountain gorilla Gorilla beringei beringei tracking tourism generates important revenue for conservation efforts but brings with it the threat of disease transmission into the gorilla population. This study quantifies for the first time aspects of encounters between gorillas and tourists at Bwindi Impenetrable National Park that are likely to contribute to the risk of disease transmission. These include how close tourists get to gorillas, how close encounters are initiated, how long they last, and the age class of gorillas involved. Tourists got significantly closer to gorillas than the park rules allow (a mean of 2.76 m, compared to the rule of 7 m), and remained close for long periods. Contacts with the gorillas most vulnerable to disease, the juveniles, were closer but of shorter duration than those with adults. Contacts initiated by gorillas were closer but shorter than those initiated by tourists. Taken together these results demonstrate that the present rules are failing, and that the risk of disease transmission may be greater than previously believed.