Fifty years ago, in 1959, George Schaller left New York for Africa to begin a study of mountain gorillas that would have lasting impact. His year of fieldwork in the Virunga Volcanoes culminated in his book, The Mountain Gorilla, published in 1963; a classic of quantified natural history, behaviour and ecology, it is still frequently cited and referred to. Research on mountain gorillas has come a long way since then. This is a brief review of that journey.

The Early Years 
After George Schaller came Dian Fossey. In 1967 Fossey arrived at Kabara meadow, Schaller's base in Congo's Parc National des Virunga. After only six and a half months, political troubles forced her to move across the border to the Rwandan sector of the Virunga Volcanoes, where she set up camp. Making a combination of the names Karisimbi and Visoke, the two nearest volcanoes, she christened the site Karisoke. It was to become one of the longest running field studies in primatology.

Fossey's first task was to habituate gorillas to the presence of observers. This process has always been easier with mountain gorillas than western populations, both because the thick ground vegetation makes mountain gorillas easier to track and therefore locate regularly, and because they have not been hunted.

Following Schaller's technique for identifying individuals, Fossey drew "nose prints" - the pattern of wrinkles and creases above gorillas' nostrils. When she was near a group of gorillas, she dropped to her hands and knees and crawled after them, giving "belch" vocalisations and mimicking their feeding sounds. These were the methods and demeanour that all researchers employed in those early years. By 1972, Fossey, with the help of newly arrived students such as Sandy Harcourt, had habituated three study groups, including the well-known Groups 4 and 5. The doors had been opened into the lives of individual gorillas whose fortunes would be tracked for decades to come. Today, researchers still observe the descendants of gorillas that Fossey first contacted. For example, the males Titus and Pablo, Ziz, Shinda, and Cantsbee, silverbacks whose names have often appeared on the pages of this journal, were all born in the 1970s. 

During this first decade, research expanded and elaborated Schaller's basic picture of gorilla social organisation and ecology, documenting the animals' day-to-day lives as well as relatively rare events such as female transfer and infanticide, and producing what came to be viewed as the gorilla blueprint. Mountain gorillas were almost entirely folivorous, living in groups with overlapping home ranges. Most individuals left the group in which they were born, with females immediately joining a lone male or another group. Dispersing males did not enter breeding groups but wandered alone until they attracted females away from other silverbacks. The resulting social structure consisted of cohesive groups held together by long-lasting bonds between males and females. In comparison, social ties between females were weak and their dominance relationships unclear. While most groups had one silverback, in those with more than one, the dominant male did most of the mating and therefore sired most offspring. It was considered, essentially, a one-male mating system. 

As for conservation, the park's guard force was ill equipped and untrained, and the involvement of conservation NGOs in the region was minimal. Karisoke Research Center was a focus of conservation effort in the Virungas and became the coordinator and implementer of regular, whole-population censuses, probably the most basic and vital conservation research there is. 

Censuses during the 1970s showed that the gorilla population had declined since Schaller's estimate. Habitat loss was the major threat, but gorillas were also being hunted for the pet and trophy trades. Then in 1978, something happened that would change everything. Poachers attacked Karisoke's longest-studied group, Group 4. The resulting deaths of two silverbacks, a female and an infant led to the disintegration of the breeding group.

The massive publicity campaigns in Europe and the USA that followed these killings led to the now famous Mountain Gorilla Project, a program that became a model for gorilla conservation across Africa.

1980s 
During the 1980s, our knowledge of the processes of group formation, and the dispersal and life histories of individuals, increased significantly, starting with the demise of Group 4 and its aftermath. Following the death of the leading silverback, all females transferred to other groups, and two infants were killed by males who were not their fathers. These tragic events underlined the crucial importance of adult males in protecting their offspring from infanticide. It would be eventually documented in other gorilla populations and would inspire theoretical developments in the study of social evolution. The remaining males of Group 4 ended up in a new study group - a band of bachelors, studied by Juichi Yamagiwa, who has since become well known for his work in Kahuzi-Biega. This all-male group would be relatively stable for years and provide another dimension to the story of gorilla society. 

It was a time for documenting and understanding variation on the basic gorilla theme. Gorillas first seen as small infants, and now reaching sexual maturity, did not always follow the same path into adulthood. For example, while some females dispersed, others remained in their natal groups with their close relatives. Some males too stayed behind, which meant that researchers could observe a breeding group with more than one silverback. Amy Vedder and David Watts studied ecological variation, showing that the gorillas' habitat varied in both food abundance and quality. One leaf was not the same as another, and gorillas ranged accordingly, favouring high quality areas.

Across Africa, studies of other populations were starting to produce data for comparison with mountain gorillas. In Kahuzi-Biega, Zaïre (now Democratic Republic of the Congo), observations of habituated Grauer's gorillas became more systematic and consistent. Caroline Tutin established her long-term study of western gorillas at Lopé in 1980, and studies in the Central African Republic and Congo Brazzaville were getting underway. Meanwhile in Uganda, Tom Butynski was directing attention to the only other population of mountain gorillas, those in Bwindi Forest. 

In the Virungas, censuses indicated that the decline in the population had been halted after 1981 with the initiation of the Mountain Gorilla Project in Rwanda, and similar conservation efforts were now underway in Uganda and Zaïre. For the first time, research focused on the human population around the park with, for example, Bill Weber's sociological questionnaires assessing attitudes towards the park and its wildlife. And in 1986, a new avenue of conservation-based research opened up with the establishment of the Mountain Gorilla Veterinary Project to manage medical interventions, such as snare removals, and to conduct routine monitoring and analyses related to gorilla health.

When Dian Fossey was murdered in her cabin at the end of 1984, many wondered if the long term research would die with her. But by then, her legacy had a momentum and reached far beyond any one individual. The Digit Fund, which would eventually become the Dian Fossey Gorilla Fund International (DFGFI), was established to ensure Karisoke's continuation.

1990s
Mountain gorilla research made impressive strides during the 1990s. Some of the most significant were developments in Uganda. By 1991, both Bwindi Impenetrable Forest and Mgahinga had been made national parks. The Institute of Tropical Forest Conservation, spearheaded by Tom Butynski, built research sub-stations in Bwindi's Ruhija and Buhoma, conducted a census, and implemented the training of Ugandan students and counterparts such as Samson Werikhe. Conservation efforts and research were intimately linked. By the mid nineties, four gorilla groups had been habituated for tourism and one for research. Studies concentrated on feeding ecology and comparisons with the Virunga population. 

The 1990s saw a general shift towards an understanding of differences between gorilla populations. As studies of western gorillas progressed in Gabon, Congo Brazzaville, and the Central African Republic, and on Grauer's gorilla in Zaire/Democratic Republic of the Congo, more data were available to ask the question: just how representative were mountain gorillas of the genus as a whole? How were they different? What became clear in the course of the decade was that mountain gorillas, especially the Virunga population, are at one ecological extreme for the genus. No other population has such limited access to fruit. Across Africa, from Bwindi westward, research showed that gorillas eat fruit when they can get it, and that this influenced ranging behaviour. The impact of frugivory on other aspects of behaviour, such as competition between females or between groups, is an ongoing topic of investigation.

With the advent of new techniques for genetic analyses, gorilla taxonomy became a hot topic. How many species and subspecies were there? While some suggested, on the basis of morphology and ecology, that Bwindi gorillas be considered a separate subspecies from the Virunga population, DNA analyses showed the two populations to be almost identical. 

The genetic studies across populations during the 1990s helped to support the growing consensus of an east-west split into two species, eastern gorillas, Gorilla beringei (including Grauer's and mountain subspecies), and western gorillas, Gorilla gorilla. Of course, there is continuing disagreement over these taxonomic questions and probably always will be.

While gorilla research and conservation programs were fast progressing in Uganda during the 1990s, they were suffering devastating setbacks in Rwanda. War broke out in 1990 and carried on with surges and lulls until the genocide of 1994 and its aftermath. War in D. R. Congo since 1996 has chronically destabilized the Virunga region, and had effects in Uganda as well. Karisoke Research Center was completely destroyed after 1994. Despite these circumstances, foreign researchers as well as several Rwandan university students conducted projects based in the Virungas, often with the sounds of gunfire and explosions in the background. Diane Doran was director of Karisoke when these troubles began.

The main gorilla study groups had continued to grow and now contained multiple silverbacks, and large numbers of females. It was the perfect opportunity to investigate behaviour in relation to these demographic changes, especially male mating competition, female mate choice, and the first documented group fission. 

New technologies came to Karisoke during the 1990s. For example, Martha Robbins and Pascale Sicotte developed techniques for collecting fresh urine for hormonal analyses of males and females. Dieter Steklis helped implement GPS technology, which was also used in Bwindi, and has transformed the mapping of gorilla ranges, vegetation and human use. It has now become a crucial tool for park rangers as well as research teams. 

Collaboration between conservation personnel and researchers, both within and between countries, increased during this decade, with the sharing of technologies (such as GPS), activities, and data. Cooperative efforts were, and still are, facilitated by the International Gorilla Conservation Programme (IGCP), established in 1991, and based on the earlier Mountain Gorilla Project. The veterinary programs in both Rwanda and Uganda developed procedures for effective interventions and for studying intestinal parasites and other pathogens of gorillas. Many of these studies are aimed at questions about the risks to gorillas of proximity to humans, be they researchers, tourists or the local population. The health of wild gorilla populations and the risk of catastrophic diseases would become a growing concern.

The 21st century
While the research center that Dian Fossey set up no longer physically exists in the forest, its activities have never ceased. Karisoke field assistants and personnel of Rwanda's Parc National des Volcans, working with research directors, Liz Williamson and, later, Katie Fawcett, have followed research and tourist groups in Rwanda throughout periods of violence. 

In this new century, researchers are harvesting the fruits of long-term data, with the help of a powerful new tool: DNA analyses. Martha Robbins and colleagues, analyzing data from as far back as the 1970s on habituated groups in the Virungas, have examined lifetime reproductive success of males and females and related it to various factors such as dispersal decisions (should I go or should I stay?) and female dominance relationships. Paternity analyses have shown that while dominant males do indeed get most of the mating, subordinate males manage to sire about 15% of the offspring. In fact, the famous Titus sired an infant while he was still turning silver, the youngest wild male known to be a father.

In Bwindi, where Robbins has been leading field studies, recent genetic work combined with population modelling has yielded valuable information about population structure, including how far males and females disperse.

But sophisticated new tools still rely on the same basic raw materials: data on where the gorillas are going and what they are doing. Methods of following groups and recording their behaviour continue much as they always have. In the Virungas, regular monitoring has documented the extraordinary growth of some groups such as Pablo's group, holding the record at over 60 members. Observations of "super groups" have provided insights into group processes such as dispersal and group fission. 

In Uganda, continuing socio-ecological studies facilitate comparisons between mountain gorillas and other species/subspecies. While fruit-eating clearly influences gorilla society, it is now clear that group structure is quite similar across Africa, with one consistent exception: the number of silverbacks per group. In mountain gorillas of both the Virungas and Bwindi, multi-male groups are relatively common (30-50% of groups), whereas in Grauer's and western gorillas, they are rare. Why? The answer is still unclear and may lie with environmental differences, life history variation, genetic factors or, most likely, a combination of forces. 

And finally, new research techniques are shaping gorilla conservation efforts. A good example is the recent extraordinary genetic census conducted in Bwindi. Individual gorillas were identified by fecal DNA analysis. The results were compared with those of a traditional census conducted concurrently, showing that traditional methods overestimated gorilla numbers. The power of a genetic census to estimate population size in areas where gorillas are unhabituated is obvious.

Given the progress of research on mountain gorillas in the last 50 years, even through the most difficult of times, there is hope that it may carry on for decades to come, as long as the gorillas and their habitat continue to be valued and safeguarded by the governments of Rwanda, Uganda and D. R. Congo. It has not been possible in this brief review to mention all of the people who have played a role in the story. Especially significant, and far too numerous to single out, are the field assistants and park personnel of all three countries, who have observed and monitored the gorillas, often risking and sometimes losing their lives in the process. Without their skill and dedication we would not have the decades of long-term data on known individuals, which is the defining hallmark of mountain gorilla research.

Kelly Stewart