How Do Gorilla Groups Work, and Who Leads Them?

A gorilla group can hold as few as two animals or as many as forty, yet almost every one of them is organised around the same figure. A single mature male, the silverback, decides when the group sets off, when it stops to rest, and how it answers a threat. If he dies with no successor in place, the group can simply dissolve.

That makes gorilla society sound like a plain monarchy. More than fifty years of field records from Rwanda's volcanoes tell a richer story, in which the females' choices and hours of daily grooming hold the group together as firmly as one male's muscle.

The short answer

Most gorilla groups centre on one silverback who leads, protects, and keeps the peace. He lives with several adult females, usually two to eight, plus their young and sometimes one or two younger males called blackbacks, for an average group of about ten. The females are unrelated, because young females leave their birth groups to join new ones, and they stay with a male who can protect them. Grooming, which tracks both rank and care, is the glue that holds the arrangement together.

Who lives in a gorilla group?

A typical group contains one silverback, two to eight adult females, their dependent offspring, and sometimes a blackback or two. Blackbacks are young males that have yet to grow the saddle of silver hair across the back. Group sizes run anywhere from two to forty, clustering around ten.

The adult females are strangers by birth. As they reach adolescence, females leave the group they were born into and join another one, a system that prevents inbreeding between close kin. The bonds inside a group are therefore built rather than inherited, and they need constant upkeep.

What does a silverback actually do?

He makes the key decisions. He sets the moment the group moves off and the moment it settles, chooses when to stand firm against danger, and defuses friction before it spreads. He is the anchor that steadies the whole group, and everyone else arranges themselves around him.

For the females, he is a bodyguard before he is a mate. A silverback who cannot hold off leopards and rival males watches his females leave for groups with stronger leaders. That is the real function of his enormous size. It works mainly as deterrence, a signal that challenging him would cost a rival more than it could win. Fights between competing males still happen, and the injuries can be severe, yet the whole point of the silverback's bulk is to keep them rare.

The females' ladder and the grooming map

The females keep a hierarchy of their own, and most of a group's everyday friction plays out among them. They compete for three things: nearness to the silverback, grooming time, and the best feeding spots. Grooming, the slow and careful picking through another animal's fur, is the main social glue in a gorilla group, as it is across most primates.

Who grooms whom is revealing. Grooming flows toward the silverback, who collects far more of it than he hands out, and the young sit on the receiving end too. Plot every grooming session in a group and you get a map of rank and of care at the same time.

What fifty years of field records revealed

Mountain gorillas have the most thoroughly documented social lives of any gorilla, thanks to the research programme Dian Fossey began in 1967 in Rwanda's Volcanoes National Park. Carried on by the Dian Fossey Gorilla Fund, that record now covers more than half a century and several generations of gorillas.

Data that deep exposes patterns a short study would miss: females moving between groups over their lifetimes, alliances between silverbacks in groups with more than one adult male, and stable individual personalities that hold across a whole life. The record has also documented infanticide. A male who takes over a group may kill the previous silverback's infants, which brings the mothers back into breeding condition sooner and hastens the arrival of his own offspring.

What happens when a silverback dies?

If a silverback dies with no established successor, his group can come apart. Without a central male to protect them and hold them together, the females usually disperse, joining other groups or teaming up with solitary males. Joining is a process in its own right. A newcomer meets tension at first, then earns gradual acceptance through grooming and time spent close to the others.

How gorilla groups care for orphans

Silverbacks in stable groups have been seen adopting orphaned infants, which is unusual behaviour for a male primate. A long-term analysis of the Fossey Fund records, published in eLife in 2021, measured how well the group cushions that loss. It followed 59 mountain gorillas who lost their mothers between the ages of two and eight, drawn from 53 years of observations, and found no detectable cost to their survival or their later breeding. After the loss, the orphans' strongest new bonds formed with the group's dominant male, whether or not he was their father, and with gorillas close to their own age.

Gorilla society is a structure that gets rebuilt every day. One male supplies the strength, the females decide whom to stay with, and the patient work of grooming keeps everyone within reach of each other.

Key terms

Silverback

The adult male at the centre of a gorilla group, named for the saddle of silver hair that grows across his back with age.

Blackback

A younger male whose back is still dark, often living in a group led by an older silverback.

Grooming

Carefully picking through another animal's fur. In gorillas it is the main social glue and a record of who ranks where.

Inter-group transfer

A young female's move from the group she was born into to a new one, the mechanism that keeps close relatives apart.

Infanticide

When a male taking over a group kills the infants his predecessor fathered, so their mothers can breed again sooner.

Related field notes

For how gorillas talk to each other, raise their young, and fill their days inside these groups, browse more Gorillas Decoded field notes.

This article is adapted from Gorilla Society, the third chapter of Gorillas Decoded, which draws on the long mountain gorilla record to show how one male, several females, and years of daily care hold a group together.