Alexander H. Harcourt

Titus represents one of many individuals whom researchers at Karisoke have studied throughout his life. Here, he is held by his mother, Flossie, on the second day of his life in 1974.

Research
The 1970s opened the doors into the individual lives of gorillas. By 1972, Fossey and others at Karisoke had habituated three groups, enabling close-range observations of known animals. Using the systematic methods of data collection that had been developed in field primatology by this time, Karisoke researchers documented and quantified the fundamentals of gorilla ecology, demography, and social organization.

A brief review of what was to become our "classic" understanding of gorilla socioecology follows. Most individuals dispersed from their natal group. Females always joined either a lone silverback or another breeding group, while males did not immigrate into breeding groups, but attracted females away from other silverbacks. The resulting social organization consisted of stable, cohesive groups held together by long-term bonds between adult males and females, while relationships among females were relatively weak (A.H. Harcourt, Social relationships among adult female mountain gorillas in Animal Behaviour, vol. 27, pp. 325-42, 1979). Dominance relationships among adult females were generally unclear, and agonistic interactions relatively infrequent. These findings could be tied to low levels of feeding competition, as well as to the dominant male's control of female-female aggression. In the groups that contained more than one adult male, rank differences between males were clear-cut and the dominant male appeared to do most of the mating. The nature of courtship and mating supported the notion that male-male competition for females found its fullest expression in contests between, not within, groups. Indeed, relations between groups were not based on resource defense, since gorillas' home ranges overlapped extensively. Rather, the nature of inter-group interactions was the result of intense mating competition between adult males.

	Thinking Point
	Experience has shown that gorillas that are the focus of research become habituated to the presence of scientists. Is it safe to assume that the behaviour observed is 'natural' and unaffected by the presence of the observers, or is it possible that the animals would behave differently in the absence of scientists?

As our understanding of gorilla socioecology increased, the growing number of studies on other primate species provided data for comparison. The "typical" primate, based on extensive studies on cercopithecines (particularly baboons and macaques), exhibited female philopatry, strong matrilineal kinship bonds, and highly structured dominance relationships. Mountain gorillas offered a sharp contrast to these findings.

Meanwhile, new field studies of orangutans in Borneo and Sumatra (e.g., H.D. Rijksen, A Field Study on Sumatran Orang Utans, 1978), chimpanzees at other sites, and bonobos were revealing extraordinary diversity in ape social organizations. In most habitats, orangutans range in a solitary fashion. The home range of a male may overlap with the home ranges of several females. Chimpanzees and bonobos are found in fission-fusion social systems, where the composition of traveling parties within a community changes depending on the food resources available and on the reproductive state of females. Although the social system of mountain gorillas was seemingly quite different, these early studies nevertheless highlighted the fact that apes shared features, such as female dispersal and at least some degree of male philopatry, that distinguished them from many other primates.

in the disciplines of animal behavior and ecology during the 1970s had a profound influence on the interpretation of gorilla behavior. While Hinde's conceptual framework described the relation between individuals' social interactions, their relationships, and the social system (R.A. Hinde, Interactions, relationships, and social structure in Man, vol. 11, pp. 1-17, 1976), socioecological models from studies of birds and mammals related ecological variables to foraging strategies, range use, and social systems (e.g., D. Lack, Ecological Adaptations for Breeding in Birds, 1968). Behavioral ecology blossomed in 1975 with the publication of Sociobiology (E.O. Wilson, 1975) providing the link between individuals' social behavior and evolutionary theory. This approach held that individuals in a group could have divergent interests and therefore, that a behavior that was advantageous for an individual was not necessarily "good" for the group. Social systems resulted from the compromises among individuals in their strategies to gain resources and mates. The view of infanticide as an adaptive strategy is a good example of how an evolutionary approach influenced our interpretation of animal behavior. Working with langurs, Hrdy (The Langurs of Abu: Female and Male Strategies of Reproduction, 1977) suggested that males may under certain circumstances benefit reproductively from killing unrelated infants. Females suffer reproductively from these killings, and she suggested that female counter-strategies to male infanticide should evolve. These have since been documented in a large number of species, including gorillas. Finally, the theory of sperm competition, a development of sexual selection theory stemming from male-male competition, put comparative data on the great apes' sexual morphology and mating behavior in an evolutionary perspective.

Conservation
Unfortunately, while research was thriving during the 1970s, the gorillas were not. The Virungas have a long history of human settlement on the edge of the gorillas' habitat, as well as incursions into the forest by people and cattle. For much of the 1970s, international conservation organizations were minimally involved in mountain gorillas, and Karisoke Research Center was the most constant and noticeable conservation presence in the forest. Its conservation activities, however, were focused on anti-poaching efforts in which patrols swept repeatedly through the forest to cut the snares that were set to catch antelopes and buffaloes (and to which gorillas are vulnerable), as well as to search for poachers' camps.

Cambridge University Press

Figure 2.  Changes in the population size of mountain gorillas in the Virunga Volcanoes region as measured by periodic censuses.

A Karisoke-based census of the entire Virunga ecosystem in the early 1970s showed that the gorilla population had declined since Schaller's estimate in the 1960s, from about 450 to about 275 animals (see Figure 2). One cause of this decline was habitat loss. Major loss of gorilla habitat occurred between 1958 and 1973, when more than 50 percent of the Parc National des Volcans (the Rwandan side of the Virungas) was cleared to allow human settlement and cultivation of cash crops (Weber, 1987, 1989). Another cause of this decline in population was the incidental as well as deliberate hunting of gorillas. In the mid 1970s, a gruesome trophy trade in gorilla heads and skulls surfaced in Rwanda, with the main market being foreign residents and visitors. This trade was behind the poacher attacks in 1978 on Karisoke's longest-observed study group, Group 4. Hunters killed two silverbacks, a female, and an infant, resulting in the eventual disintegration of the breeding group. The massive publicity campaign in England and in the USA that followed these killings resulted in the now famous Mountain Gorilla Project, a program that became a model for gorilla conservation in other parts of Africa.