Genetic census reveals increased but uneven growth of a critically endangered mountain gorilla population

Monitoring changes in the population dynamics of endangered species is crucial to effective conservation strategies. The mountain gorilla population of the Virunga Massif has been the subject of intensive conservation efforts, research and several censuses over the last 40 years, but the region has also been affected by political instability and war. Here we present results from the 2010 census, which was the first to utilize genetic analyses of fecal samples for the entire population. The genetic analyses improved the accuracy of the population estimate by identifying several instances in which gorillas otherwise would have been undercounted or double-counted. The population was estimated to be 480 individuals; including 349 individuals found in 24 groups that were habituated for research and tourism, 101 individuals found in 12 unhabituated groups, fourteen solitary males, and a correction factor of sixteen for undetected infants. The population has increased by 26% since 2003 (an annual rate of 3.7%) and it has almost doubled since 1981. Nearly all of the increase can be attributed to a relatively higher growth rate in the habituated groups from 2003 to 2010, and in all five of the previous intervals between consecutive censuses. Nonetheless, it would be imprudent to habituate additional groups due to the concomitant risks of disease transmission from humans, behavioral disturbance and potential vulnerability to poaching. The results show that it is possible for conservation efforts to succeed even under difficult conditions, while highlighting the continuing challenges of managing a wild population of both habituated and unhabituated gorillas.