Umusatsi: An Independent Gorilla Mother

February 29, 2011

Umusatsi: An Independent Gorilla Mother

UmusatsiMost female mountain gorillas stick close to the protection of a dominant male and his followers, especially while the female is caring for an infant. Not so Umusatsi, who has shown a penchant for wandering off by herself with her infant son Rwema for days or even weeks at a time, while anxious Karisoke trackers search for the pair.

Umusatsi was born into Pablo’s group on May 15, 1984. In early 2007 she transferred with two other females to what was then known as Beetsme’s group, though already led by silverback Kuryama. Her 2-year-old infant had died the previous November, and trackers reported that following the death she “seemed to have become a passive member of (Pablo’s) group, rarely interacting with other individuals.” However, she was gradually accepted as a member of her new group and seemed off to a new start. In September 2007 she gave birth to Rwema.

RwemaIn the spring of 2011, Umusatsi had weaned the 3-and-1/2-year-old Rwema and was mating with Kuryama, then unaccountably left the group on her own — four times. It would not be unusual for a newly fertile female to transfer from one group to another seeking new reproductive opportunities, but in this case Umusatsi took Rwema with her each time and did not join another group – putting her infant at risk of infanticide by any solitary male or male from another group who might encounter them.

While Umusatsi and Rwema were on their own for four days in late May, they were sighted dangerously near an interaction between Isubukuru’s group and Kuryama’s. Finally they returned to Kuryama’s group, only to disappear again for several days in June following another inter-group interaction. They left again in June for a few weeks but returned.

A few other females from the research groups also wandered away on their own at times during the fall of 2011. Two, Ginseng and Kubyina, weakened and died. Umusatsi and Rwema went missing in November, but were found in good health, far from any of the gorilla groups and kilometers away from Kuryama’s group – but staff were not available to continue to follow them when they wandered off again. Everyone was relieved when they returned to Kuryama’s group after an absence of three weeks, just as a patrol was being organized to look for them.

The saga continued in early February of this year when the pair left for about two weeks during a time when the field staff were occupied with a crisis in another group and could not follow Umusatsi. Again, she reappeared on Feb. 16. The two silverbacks in Kuryama’s group, Kirahure and Vuba, made frequent displays at Umusatsi upon her return. It remains to be seen whether she was sufficiently impressed to remain with them for good this time.

Umusatsi and RwemaThe field staff have become somewhat accustomed to Umusatsi’s unusual behavior, despite their concerns for her safety and Rwema’s, because she is quite experienced in the forest at age 27 and seems to travel with confidence. We will follow her next move with interest. “Gorilla behavior is sometimes unpredictable and may not have a clear explanation,” as Gorilla Program Manager Veronica Vecellio observed during one of Umusatsi’s excursions last year.