Beetsme: Odyssey of a Silverback
Because of the long life span and social complexity of gorillas, it has taken researchers at the Karisoke Research Center decades to untangle the different paths and strategies that individuals can follow in the course of their lives.
The life of a male gorilla is particularly difficult to predict. Equal numbers of males and females are born but because groups consist of only one to two silverbacks with many females, there is inevitably an excess of males. Upon maturation, males are often expelled from their natal groups. These "extra" males become solitary and try to attract females from other groups. Sometimes a male remains in its natal group as a tolerated subordinate silverback. However, many males may never form a group or reproduce.
Life histories of male gorillas are affected not only by strength, fighting ability, and social skills, but also by events that unfold in the local gorilla groups, such as the death of a leading silverback. The misfortune of one individual may be a lucky break for another.
Beetsme passes on
Recently, 25 years of observation of one male gorilla came to a close when silverback Beetsme died on June 15, 2001. Beetsme was first observed in 1975 as an unidentified individual traveling with silverback Peanuts. He was next seen in 1976 when he transferred into Group 4, and acquired his name when Dian Fossey was asked about his identity and, seeing him for the first time, replied "Beat's me!"
Beetsme remains unique as the only known case of an adult male gorilla joining a breeding group. (Unknown males are not tolerated because of high competition among males for females.) In fact, for a time researchers thought he was a newly acquired female. One researcher noted early on that "this female sure does chest-beat like a male." His true gender was determined when he began to grow and develop a silver back. While in Group 4, Beetsme played a largely peripheral role, perhaps to avoid aggression from other males in the group.
His group breaks up
The next major life event for Beetsme came in 1979 when Group 4 disintegrated following the poaching death of the two silverbacks of the group, Uncle Bert and Digit, along with female Macho. Beetsme was not yet fully mature and did not have strong relationships with the adult females of the group, so he was unable to lead the group.
The adult females emigrated to other groups and Beetsme was left with Titus and Tiger, two immature males. They eventually joined up with Peanuts, who was then accompanied by three other males. While this all-male group provided an environment for individuals to interact with one another and develop social skills, it did not favor reproduction.
Beetsme's luck turned again in 1985 when the only silverback in a neighboring group, Nunkie, died. The remaining members of Nunkie's Group merged with the bachelor group containing Beetsme. But due to the large number of males competing for the females, coexistence seemed impossible. A few months later this untenable group split: Peanuts was left, once again, with only male companions while Beetsme remained with the females along with Titus, his long-time companion.
Heads group for four years
At 19 years of age Beetsme achieved the status of dominant silverback of a group with several females. Beetsme's reign as the dominant silverback of his group lasted only four years until 1989, when Titus, now a large, fully mature silverback, began to challenge the alpha male position.
Beetsme's luck continued in that the turnover of dominance rank was not particularly aggressive (although several spectacular fights were witnessed) and Titus did not evict Beetsme from the group. It seemed a male bond was established during their bachelor days together. Beetsme's remaining in the group was probably facilitated by his strong relationships with several group members, in particular the high-ranking female, Papoose. Beetsme and Titus occasionally continued to work as a team during intergroup encounters to prevent any of "their" females from emigrating.
Female transfers only occur during group interactions. Often these interactions are chaotic, with silverbacks strutting, breaking branches, chest-beating, and making as much of a display of strength as possible. Females sometimes take advantage of the confusion and transfer to the other group or lone silverback.
Titus and Beetsme split work
Beetsme and Titus employed a different strategy. They avoided contact between the females of Beetsme's group and the intruding group or marauding silverback. They achieved this by splitting duties: Titus would leave the group and confront the threatening group/silverback while Beetsme remained behind with the females, well away from the hubbub of the interaction.
Using this strategy, Beetsme and Titus were able to rebuff the intruders and at the same time prevent possible female transfers out of their group. In fact, over the last 10 years, only 3 of 9 adult females transferred out of Beetsme's Group (Umuco, Ginseng and Pasika). Future work analyzing female transfers will tell if this 'splitting duties' strategy is significantly more successful than others.
During the last decade of his life, Beetsme saw his group increase in size from 14 to 26 individuals, including over a dozen births. It is uncertain how many were sired by Beetsme or Titus, but a paternity determination study is underway which will enable us to calculate their relative reproductive success.
Alone at the end
Sadly, the final few days of Beestme's life were spent alone. After a presumed fall, Beetsme broke a bone in his heel and this handicap prevented him from keeping up with the group as it traveled. It is unusual for a group to leave one of their own behind, but in the later years of his life Beetsme was often peripheral, distancing himself with his night nest sometimes 50 meters from other gorillas' nests.
The Beetsme bonding exception
Beetsme has contributed to our knowledge of male gorilla life histories in many ways. He has shown us that there is always an exception to any rule (e.g., males are never allowed to join established heterosexual groups). He has illustrated the importance of not only male-female relationships, but also bonds between males. Beetsme has also enabled us to see how the fortunes of a male gorilla can change several times in the course of life.
Finally, Beetsme has also informed one piece of the life-history puzzle of mountain gorillas: longevity. Because he was first observed as a blackback (~10 years old), we don't know his exact age, but Beetsme was about 36 years old when he died. Even this estimate is useful because so little is known about the life history of wild gorilla males anywhere.
Though as researchers we always aspire to be detached from our subjects, to peer into their daily lives with a cold objectivity, in practice such professed detachment is essentially impossible when our subject is a social ape with an intelligence and emotions strikingly like our own. So we quite naturally rejoice when they become mothers and fathers, anxiously follow their quarrels, and, as in Beetsme's case, mourn their death. Scientific detachment, strictly speaking, is left to our smart metallic companions who crunch the numbers and abstract objective reality from the duly recorded daily events that comprise the gorillas' lives.
It should be no surprise then that we miss Beetsme. All who had the privilege of studying him, the Karisoke trackers and many researchers, were struck by his distinctive personality (or temperament) that lent a special character to his group.
Faustin Barabwiriza, who has worked for Karisoke for over 30 years, spent the majority of the last 20 years following the group of which Beetsme was a member. Like other trackers and researchers, Barabwiriza was keenly aware of what he described as Beetsme's "dual character": Beetsme was not fond of people and hence did not tolerate human observers for long periods of time, giving frequent "cough grunts" (a threatening or warning vocalization) to those who approached him. On the other hand, Beetsme was exceptionally tolerant of his fellow group members, including the male Titus who, as recounted earlier, eventually deposed Beetsme from his position as dominant silverback. The socially tolerant, non-aggressive character of Beetsme resulted in a relaxed, calm atmosphere in the group as a whole (though he could be a grumpy old bugger towards researchers and trackers).
Asked for his feelings about Beetsme after his death, Barabwiriza stressed that he would never be able to forget Beetsme. He still thinks of him very regularly and he misses him very much. He was very fond of Beetsme because their relationship went back such a long way and because of the kind and gentle nature he saw in his friend the silverback.
We are deeply grateful to Beetsme for his having tolerated for so many years our probing eyes, camera lenses, and other scientific paraphernalia, without which we would not now have such a profound understanding of the trial and tribulations over the course of a gorilla's life. We hope to repay this debt by rededicating ourselves to the task of protecting and conserving his surviving relatives, group members, and the larger population that gave rise to them all.
Martha Robbins, Ph.D., Max Planck Institute for Evolutionary Anthropology;
H. Dieter Steklis, Ph.D., DFGFI, Vice President and Chief Scientist;
Netzin Steklis, DFGFI, Scientific Information Resources;
Liz Williamson, Ph.D., DFGFI, Karisoke Research Center;
Marc Pierard, DFGFI, Karisoke Research Center.