February 4, 2011

Silverback Inshuti Attracts Another Female

The gorillas of Inshuti’s group – one of the groups we monitor from the Karisoke™ Research Center in Rwanda – were unusually excited on the morning of Jan. 22. It was clear that something had happened. Dominant silverback Inshuti was beating his chest repeatedly, while moving around one of the females. A closer look by our trackers revealed that the female was not an established member of the group but was in fact a female from Titus’ group, named Umwana.

The transfer was determined to have occurred during an interaction between the two groups on the previous evening. The interaction itself was not observed by our trackers, but the site where the two groups faced each other was clearly marked by a large area of flattened vegetation and broken branches.

Now, Inshuti was trying his best to impress the new female. He showed off his massive body size, standing in front of Umwana and stiffening his arm and leg muscles. The other three females of the group were obviously curious about the newcomer, observing her from a few meters away, but did not interfere with Inshuti’s performance.

One kilometer away in another area of the mountain forest, Rano, dominant silverback of Titus’ group, was clearly “disappointed” by his loss. He was isolated a few meters apart from the rest of the group and made some call vocalizations addressed to Umwana, but he was too far away to be effective. After a few hours he joined his remaining female, Imvune, and from that moment on has not left her side. We believe he will now focus all his attention on keeping Imvune with him.

Umwana was the first female to join Rano when his leadership started. She stayed with him for one year, during which they were usually in close proximity, apparently sharing a strong bond. Yet, Umwana failed to get pregnant, which may be the reason why she decided to transfer to another group. She is 27 years old, not young but still in the age range to produce more infants.

Inshuti’s excitement lasted many days after Umwana’s transfer. He never moved more than five meters from the female, displaying his strength with chest beats and breaking big branches, as well as uttering frequent sexual vocalizations. Umwana has been observing this performance calmly, taking her time to become acquainted with the new situation. She still seems hesitant to interact with group members other than Inshuti.

During the three years since Inshuti formed his group, he has gained – one by one – a total of four females. One has already given birth and one is currently pregnant. Without doubt, Inshuti has made giant steps to satisfy his ambition to become a significant group leader, after leaving his previous life as a lone silverback.

Submitted by Veronica Vecellio, Karisoke™ Research Center, Gorilla Program Manager