The Mountain Gorilla

The Mountain Gorilla subspecies is found in only two isolated subpopulations in Rwanda, Uganda, and the DRC. The Virunga subpopulation was estimated at 380 individuals in 2003, an increase from 320 in 1989 (Gray et al. 2006). Approximately half of the subpopulation is mature individuals (Kalpers et al. 2003; Gray et al. 2006). However, all population growth in the Virungas between 1989 and 2003 has been limited to one sector of the population, the four gorilla groups in perhaps ecologically the richest area, which is also relatively well protected (Kalpers et al. 2003; Gray et al. 2006).

Not only do unhabituated (and therefore less well-protected) groups have a lower ratio of juveniles to adults, but the current rate of growth of the whole population is lower than that during the 1980s (Kalpers et al. 2003). Additionally, a resurgence in poaching and killing of gorillas (approximately 3% of the entire Virunga subpopulation in 2007: see below) directly limits population growth and emphasizes the fragile nature of this small population.

While the G. B. Beringei subpopulation in Bwindi Impenetrable National Park was believed to have increased from about 300 gorillas in 1997 to 320 individuals in 2003 (McNeilage et al. 2006), a census in 2006 that combined genetic analysis of the entire population with traditional census methods revealed that there are only approximately 300 individuals in Bwindi (Guschanski et al. In review). These new results do not lead to the conclusion that the population has declined in size; instead, due to the ‘sweep census’ method used, it is not possible to put error estimates around the population estimates and therefore it is difficult to assess how the population size has been changing over time.

In total, the subspecies G. B. Beringei has only approximately 680 individuals remaining in two isolated populations.

G. B. Graueri
In 1995, the population of G. B. Graueri was estimated at 16,900 animals (Hall, Saltonstall et al. 1998; Hall, White et al. 1998). In the last decade, it is believed that the total population has declined dramatically, as the lowland populations have been progressively fragmented and reduced (Hart and Liengola 2005; Hart et al. 2007). Many populations have disappeared in the last 30 years (comparing Schaller 1963 and Hall, Saltonstall et al. 1998); for example, Itombwe lost about half of its subpopulations between 1960 and 1996 (Omari et al. 1999). Their habitat continues to become fragmented and discontinuous; the current occupancy range for Grauer’s Gorilla is estimated at 21,600 km², a decline of 25% from surveys completed in 1959 (Mehlman 2008). However, data are lacking to determine the extent of decline, apart from in the uplands of Kahuzi-Biega National Park, where the population dropped from an estimated 270 in 1996 to only 170 animals in 2000 (WCS 2000).