"Violent encounters between social units hinder the growth of a high-density mountain gorilla population" by Jean Paul Hirwa, MSc

I would like to take you on a 50-year journey of mountain gorilla conservation and research. Intense conservation measures have led to the remarkable recovery of the Virunga mountain gorillas from a low of ~260 individuals to 604 in 2016. This unique success in great ape conservation comes with new challenges. The growing numbers of gorillas living in a small isolated forest fragment have increased the population density, which may result in food shortage and a higher risk of disease outbreaks and thus limit population growth. The analysis of 50 years of mountain gorilla data reveals that social behavior changes rather than ecological factors affected the growth of a subpopulation in a high-group density area where some of the highest growth rates were documented between 1980 and 2010. A sudden increase in social group density observed in 2007 led to a threefold increase in the rate of encounters between social units (groups and solitary males). These encounters can involve fights between silverbacks and caused lethal injuries in seven cases. Infants are also often targeted during these inter-group aggressions, which caused a fivefold increase in the rate of infanticide. As a consequence, the annual subpopulation growth rate slowed between 2000 and 2017 from 5.05% to 2.37% but remains positive. The increase in infanticide alone explains 57% of this decline. Our findings highlight the complex relationship between population density and growth in mountain gorillas and hold important implications for the management of this island populations, which I will discuss in my talk.



Jean Paul Hirwa is currently the gorilla program manager at Karisoke Research Center, a program of The Dian Fossey Gorilla Fund in Rwanda, overseeing all the gorilla monitoring and protection activities. This involves management of Fossey Fund field staff including gorilla trackers, antipoaching teams and research assistants. He coordinates daily monitoring of every individual gorilla monitored by Karisoke and oversee long-term data collection on gorilla demography, behavior and ranging patterns.  

He joined the field of gorilla conservation 10 years ago first as an intern with the Mountain Gorilla Veterinary Project (Gorilla Doctors) then as a research assistant with Karisoke. He was involved in research on the demography, behavior and ecology of mountain gorillas as well as the threats that gorillas face in their habitats. Beside his work with mountain gorillas in Rwanda, he supported and interacts with Fossey Fund teams working in the conservation of Grauer’s gorilla in D.R. Congo. 

He completed his master’s studies in 2017 in Tropical Biodiversity and Ecosystems thanks to a scholarship from the European Commission through an Erasmus Mundus master’s program (TROPIMUNDO). This program allowed him to attend courses at different universities and higher learning institutions in France, Cameroon and Belgium. For his thesis research, he studied foragingrelated interactions between arboreal monkeys and terrestrial mammals on Barro Colorado Island in Panama. 

Jean Paul is committed to contribute in conserving biodiversity in general and gorillas in particular through research, active protection, law enforcement as well as working with communities neighboring the gorilla habitats.