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Historic gorilla group faces silverback drama

By Veronica Vecellio, Gorilla Program Senior Advisor

This piece is part of a series of articles presented by the Fossey Fund’s Gorilla Program Senior Advisor Veronica Vecellio, focusing on the mountain gorilla groups that the Fossey Fund protects and studies every day in Rwanda. Veronica has worked with these gorilla families for nearly 20 years and shares her deep knowledge and insights about their lives.

The mountain gorilla group named after former silverback Pablo is the most historic mountain gorilla group ever studied. Established in 1993 when Group 5 split into Pablo and Shinda groups after the death of dominant male Ziz, Pablo group has been monitored longer than any other gorilla group, starting with Dian Fossey’s observations in 1967.

What has set Pablo group apart throughout the years is the remarkable stability of its core members, which is why the group’s name has never changed despite changes in dominance. This cohesion is unusual among gorilla groups, as they often experience radical changes in group composition when the dominant male position changes.

Pablo group history

Namesake Pablo led the group only briefly, before it was taken over by the remarkable silverback Cantsbee, who was a highly effective leader. Cantsbee led the group for a record 25 years and set many other records as well – siring the most offspring, growing his group to an incredible 65 members and becoming the oldest male gorilla ever monitored.

An interesting pattern seen in the group was one started by Cantsbee, in which there was a dominant male and a supportive subordinate. This is what happened when Cantsbee took over from Pablo, with Pablo remaining a loyal supporter throughout the rest of his life. This alliance was a key to the group’s long-term success.

History repeated itself when Cantsbee, in his old age, supported his son Gicurasi to prepare for leadership, allowing Gicurasi to be a primary mating partner for a decade even though he was the second in command until Cantsbee’s passing. And Gicurasi led the group ably after Cantsbee’s death in 2017.

And a changing present

We have now just witnessed an unusual year in Pablo’s group, with some intriguing events in male gorilla dynamics. Namely, Pablo’s group is facing another dominance challenge, this time perhaps occurring prematurely.

Since last November, we have been observing an attempted shift in dominance from the second-ranking silverback, Ubwuzu, a 17-year-old who is a nephew of Cantsbee (and cousin of Gicurasi). He is physically stronger than the 28-year-old Gicurasi, who seems to have faced some health issues. As Gicurasi lost some physical strength, Ubwuzu grasped the opportunity to assert his dominance.

This shift has been evident through physical displays as well as non-physical displacement behaviors. Although Gicurasi has resisted at times, he has ultimately accepted the subordinate position. Among the other males in the groups, this dominance challenge has resulted in conflicts, including physical fights and shifting alliances. In fact, Ubwuzu has instilled fear in many of the males, who now align themselves with Gicurasi instead

Most of the females have accepted Ubwuzu’s dominance, but some, like Teta, remain loyal to Gicurasi. We have observed subgrouping around the two males, reminiscent of the situation between former dominant Cantsbee and his second-in-command, Pablo.

The females in the group are all relatively young. Four of them have infants, while another two are expected to give birth soon. The presence of six infants and juveniles brings joy to the group, maintaining an active and playful atmosphere despite the ongoing conflicts among the adults.

In another twist, Gicurasi is currently showing signs of recovery, and his loyal gorilla companions often remain close to him. We are curious to see if Ubwuzu’s more aggressive leadership style will stabilize into a calmer situation or if he will continue to rely on displays of physical strength.

We hope to witness Ubwuzu’s successful development with the guidance of the more experienced Gicurasi and the support of all the other males and females. Once again, Pablo’s group, now composed of 18 gorillas, provides us with a unique window into the intricate social life of gorillas, a unique privilege we have here at the Dian Fossey Gorilla Fund.