A CENSUS OF THE EASTERN LOWLAND GORILLAS GORILLA-GORILLA-GRAUERI IN KAHUZI-BIEGA NATIONAL-PARK WITH REFERENCE TO MOUNTAIN GORILLAS G-G-BERINGEI IN THE VIRUNGA REGION, ZAIRE

A population census of eastern lowland gorillas Gorilla gorilla graueri was conducted in the original part of Kahuzi-Biega National Park, Zaire. At least 258 gorillas (25 groups and nine solitary males) were estimated by bed counts to have survived within the Park in the 1990 bamboo season. In comparison with results of the previous censuses, conducted between 1978 and 1979, the population showed a slight increase. The percentage of immature individuals in the population indicates that gorillas still maintain a healthy population, but mean group size has decreased markedly. Although gorillas expanded their range in the 11 years between the surveys, they have still tended to concentrate in the central well-protected area of the Park, possibly stimulating frequent transfer of females between groups or from groups to solitary males, resulting in the decrease in group size. Recent social changes recorded from observations of habituated groups tend to support this interpretation. Human disturbance in the bridge zone between highland and lowland forests prevents gorillas from making contact with their neighbours and reduces the possibility of outbreeding within the Park. Reference is made to the more detailed censuses of the mountain gorilla G. g. beringei. More international attention will be needed to increase conservation activity to protect gorillas from the hazards of human disturbances in this area.