Infant Killing May Be Necessary
The collapse of Group 8 threw a spotlight on the grisly practice of infanticide. The matriarch Koko died, and Rafiki with a new mate, Macho, sired a female infant, Thor. Rafiki died before Thor was a year old. The old male left behind a silverback son, Peanuts, who tried to take his father's place safeguarding Macho and his infant half sister. But during an interaction with Group 4, Thor was killed by Uncle Bert.
Though victims usually die almost instantly as the result of one severe and crushing skull bite, accompanied by a deep bite in the lower groin, the initial concept of gorilla killing gorilla was too horrid for me to accept. Yet I now believe infanticide is the means by which a male instinctively seeks to perpetuate his own lineage by killing another male's progeny in order to breed with the victim's mother. In some cases the stratagem seems necessary to maintain a healthy degree of exogamy, or outbreeding. Infanticide has accounted for the deaths of 6 out of 38 infants born over a 13-year period.
Rafiki's mate, Macho, stuck with Peanuts for five months. Then, after fierce interactions between Peanuts and Uncle Bert, dominant silverback of Group 4, Macho joined up with him. Peanuts was cut adrift as the only individual left from decimated Group 8.
As if the fragmentation of Group 8 was not loss enough, the tragedy that soon overwhelmed Group 4 provided a casebook example of group disintegration. With Uncle Bert as leader, and with the help of two younger males, Digit and Tiger, Group 4 accepted another male, Beetsme. This was the first—and so far only—recorded male immigration to a group. Digit, now maturing into a full-fledged silverback impregnated the adult female Simba II. Digit helped Uncle Bert defend the group, and the two silverbacks were amiably compatible. Although the presence of Tiger, more closely related to Uncle Bert, would prevent Digit's ever becoming the dominant silverback, I thought it unlikely that he would abandon Group 4 as long as he was needed.
In the daytime on New Year's Eve 1977, Digit was indeed needed. As watchdog of his natal group, he held off six poachers and their dogs who unexpectedly ran into the gorillas at the end of their trapline set for antelope in the saddle area west of Mount Visoke. Allowing the other 13 members of his group to escape, Digit took five spear wounds, yet in ferocious self-defense managed to kill one of the poachers' dogs before he died for his group.