Fri, January 12, 2018

Solo gorilla mother joins lone silverback

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For seven months, mountain gorilla mother Pasika did something remarkable. Normally, female mountain gorillas spend their entire lives in groups, relying on an adult male silverback to protect their young. But when Pasika’s group dispersed after the death of the silverback last May, she never transferred to another group, which is what would normally happen. Instead she traveled alone in the forest with her 1-year-old infant, Mashami.

Pasika and Mashami

Pasika had good reasons for this behavior. When females with infants transfer to a new group, conflicts often arise involving the new silverback, leading to the death of the infant. This is called “infanticide” and is a common male reproductive strategy seen in many mammal species. It serves to bring the female quickly back into reproductive condition to mate with the new male, which otherwise wouldn’t happen until the infant is completely weaned (at about 3 years old in gorillas). This exactly what happened with the other mother who lived in Pasika’s group – her infant was killed when she transferred to another group right away.

Initially Fossey Fund trackers and scientists continued to follow Pasika and Mashami on a daily basis, but she was clearly trying to avoid being noticed by both other gorilla groups and human observers, whom she knows well.  Even without daily tracking, Fossey Fund staff still saw her from time to time in the forest, and she and the infant seemed to be in good health.

At the end of December, Pasika was seen again by one of our tracking teams, but this time she was with a lone silverback and Mashami was not with them. Our field staff identified the lone silverback as Turatsinze, who has been on his own since 2006, when he left a large group that is followed daily.

Silverback Turatsinze (left) and Pasika (right)

Although Fossey Fund staff have not located the body of infant Mashami, it is quite clear that the infant would no longer be alive.

“Pasika’s story proves that even after 50 years, there is still so much to learn about one of our closest living relatives,” says Dr. Tara Stoinski, President and CEO and Chief Scientific Officer of the Fossey Fund.

“Although we expected such an outcome, we were also all rooting hard for Pasika to be able to succeed in protecting her infant somehow, since she managed for so long without a group. It is always heartbreaking for our field staff when any gorilla dies, and this time it was especially difficult,” says Felix Ndagijimana, director of the Fossey Fund’s Karisoke Research Center and programs in Rwanda.

The fact that Pasika likely lost Mashami due to interacting with a solitary male is not surprising. Solitary males are often harder to detect than groups and so it may have been easy for him surprise Pasika, who clearly had been avoiding contact with other gorilla groups.

Now that Pasika is with a silverback, Fossey Fund teams will follow them daily and report on their progress. Staff are hopeful that the group will grow, both with the addition of more females and eventually with new infants as well.

 

 

 

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