The effect of age and size on a male gorilla's (Gorilla gorilla gorilla) role within the social group
Lambert, Joanna E.
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In their natural environment gorillas form social groups that are typically composed of several adult females and their young offspring, one or two young blackback males, and one fully mature, socially dominant male. A gorilla male is mature by approximately his thirteenth year, by which point he has attained his full weight and size and a dorsal saddle of silver-white pelage. The so-called silverback's dominace is reflected by the fact that he alone will mate with the group's sexually receptive females. The silverback can also intimidate other group members and it is his proximity that is most often sought out by other group members. This project attempts to identify the characteristics required by a male gorilla to be socially dominant. This was done by studying three captive groups of western lowland gorillas (Gorilla gorilla gorilla). One study group is housed at the Brookfield Zoo and has as its oldest male a nine-year- old blackback. Of the two other groups, one has an eight-year-old blackback as its oldest male member, and the other a twenty-four-year-old silverback. These last two groups are housed at the Lincoln Park Zoo. Approximately 180 hours of observational data were collected over a four-month period spanning from the fall of 1990 to the winter of 1991. Particular attention was paid to the approximate distances between the male and the other group members, and affiliative and agonistic behavior directed by other members of the group to the male as well as affiliative and agonistic behaviors directed by the male. It was predicted that a male's age and size play a significant role in his ability to dominate. As predicted, the younger blackback males, Ndume and Gino, were not socially dominant in their groups. Their proximity, in general, was not sought out by other group members and they were the recipients of much more aggressive behavior than they directed toward others. The fully-grown silverback, Frank, was found to be the most dominant member of his group. It was his proximity that was most often sought out and he received no agonistic behavior.