Western Lowland Gorillas—New research on their social structure and possible implications for the transmission of ebola virus

It is good to see old friends in print. This time it is the Western Lowland Gorillas we were privileged to visit and watch at Ngaga in the Odzala-Kokoua National Park of the Republic of Congo (Congo, Brazzaville) nearly five years ago (see my post of 18 August 2014).

We visited two groups just a few miles apart and it is the interactions that occur between the three group in the immediate vicinity of Ngaga that is the subject of a paper just published in Proceedings of the Royal Society.

I cannot overemphasise the enormous amount of work that went into this study done between 2013 and 2017. Behaviour of the groups was monitored on approximately 305 days each year. The trackers (who move at speed through the forest) located the groups each morning. Every individual gorilla can be recognised by the trackers and researchers. Notes were made of their behaviour for an average of two hours per day, itself a difficult undertaking because of the dense vegetation. And the authors do not even mentikon the sweat bees.

The behavioural work was done by Magdalena Bermejo (who heads the whole project in the Republic of Congo) and Germán Illera, with help from the same trackers who took us from the lodge to the groups of gorillas.

In addition to the behavioural observations, gorillas over a wide area were genotyped from samples of their faeces collected from the nests they build and occupy at night.

Previous observations on Western Lowland Gorillas (Gorilla gorilla gorilla) at bais (open grassy clearings often surrounding a body of water) suggested a very different behaviour from the Mountain Gorilla (G. beringei beringei). Groups of the former met without aggression—in marked contrast to encounters between group of the latter. In Ngaga, an area without bais, these observations were not only confirmed those but indicated a dynamic community structure. In the words of the authors:

Both approaches revealed a social system much more dynamic than anticipated, with non-aggressive intergroup encounters that involved social play by immature individuals, exchanges of members between groups likely modulated by kinship, and absence of infanticide evidenced by infants not fathered by the silverback of the group where they were found. This resulted in a community composed of groups that interacted frequently and not-aggressively, contrasting with the more fragmented and aggressive mountain gorilla (G. beringei beringei) societies. Such extended sociality can promote the sharing of behavioural and cultural traits, but…

The but refers to the disease that has devastated local gorilla and human populations, including the area studied—ebola. The authors make the point that interaction between groups could promote the rapid transmission of the virus:

Social behaviour may thus have greatly contributed to the massive impact of past Ebola outbreaks that have resulted in an increase of the threat level for the species, raising major conservation concerns about population declines in the future. Understanding group dynamics in social species is of utmost importance when coming to model the transmission of pathogens such as Ebolavirus. However, since the high mortality imposed by outbreaks is likely to select against this social behaviour, its persistence in W[estern] L[owland G[orilla] implies that either such massive die-offs may have been rare in the past, or that the associated benefits outweigh the disadvantages. In any case, the peculiar social behaviour of western lowland gorillas is an outcome of its evolutionary history and will definitively impact its fate.

I do wonder though whether the dynamic social structure and outbreeding may actually ensure a higher degree of immunocompetence of individuals. In other words, and turning the argument round, whether the social structure is actually protective to individuals exposed to potentially lethal infections.

Here is a link to the video included in the paper.

And here  again are my videos of the gorillas at Ngaga:

Forcina G, Vallet D, Le Gouar PJ, Bernardo-Madrid R, Illera G, Molina-Vacas G, Dréano S, Revilla E, Rodríguez-Teijeiro JD, Ménard N, Bermejo M, Vilà C. 2019. From groups to communities in western lowland gorillas. Proceedings of the Royal Society B 286: 20182019. http://dx.doi.org/10.1098/rspb.2018.2019 

A Visit to Gorillas in the Congo

One of my earliest memories is of the first non-domestic animal I saw—a gorilla, ’Alfred’ at Bristol Zoo in summer 1946. The snapshot in my brain has the zoo entrance to the left and Alfred’s cage in front of me. My great (grand in genealogical terminology) uncle and aunt and my grandparents are to my left and my parent are to my right. Alfred is dragging a piece of sacking from left to right.

Alfred was an animal celebrity and a source of great pride in Bristol where he lived from 1930 until he died in 1948.

Another gorilla but this time a dead one also made a strong impression on a little boy.‘George’ (I cannot remember his ever been called this in the 1950s) was in the natural history museum at Wollaton Hall. Mounted impressively, upright, hanging on a tree, with his teeth bared and reproductive organs in full view (small remember in the gorilla) he towered above the visitors and this small boy can remember being more than a little scared every time I was taken to see him (probably two or three times a year). George is still there but Wollaton Hall as a natural history museum is a shadow of its former self and confirms my belief that museum display professionals must learn to leave things alone. This gorilla, I read now, was bought by Nottingham Corporation from the 1878 Paris Exposition held to mark the recovery of France from the Franco-Prussian War.

The next time I saw Alfred he was stuffed and on display in the Bristol’s museum, still the cause of great civic pride as recounted by Hannah Paddon in Sam Alberti’s The Afterlives of Animals. That was in 1957. Bristol Zoo went on to have other gorillas in the 1950s and I took photographs of the new accommodation when I went to my last visit to Bristol Zoo in 1963.

Bristol Zoo Gorilla House, 1963

As I wrote in my post of 16 June, the privilege of being able to visit groups of Western Lowland Gorillas and observe the other mammals, birds, reptiles and amphibians in the Congo Basin is an experience of a lifetime. In the middle of May we were with a group of ten clients of Naturetrek in the camps in the Republic of Congo run by Wilderness Safaris, Ngaga and Lango, 340 miles from Brazzaville, both in or adjacent to the Odzala-Kokoua National Park.

At Ngaga we divided into parties of two or four and visited two groups of gorillas, each headed by a silverback, ‘Jupiter’ and ‘Neptune’. These gorillas were habituated by Dr Magda Bermejo and her colleagues. Because of the effects of outbreaks of ebola on the population, the IUCN classification of the Western Lowland Gorilla is 'critically endangered’.

Filming was difficult through the thick vegetation. The camera was often at arms length and liable to shake. However, the footage below also shows the dense Marantaceae foliage, a major source of food for the gorillas, the environment in which they live and the sweat bees they have to put up with. What the video does not show is a female gorilla moving behind us and coming closer to see what we were about. She had a good look from a few yards away and then moved on to join the rest of the group as they climbed into the tops of the trees.

I shall never forget the sight of Neptune climbing the tree with consummate ease—and even striking the pose of the long-dead George. But the large tooth display was the result of a languid yawn as he paused before climbing even higher.

There is no greater privilege in the world than seeing a group of lowland gorillas in the wild in the Congo—sixty-eight years after seeing that unfortunate but great ambassador for gorillas, Alfred.