Mon, May 8, 2017

Gorilla mothers deal with missing silverback

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The Dian Fossey Gorilla Fund staff are concerned about an unusual situation in one of the mountain gorilla groups we follow every day, because the one and only adult male – the leading silverback – has left the group, with two mothers and their infants now having to fend for themselves without his protection.

Mountain gorilla groups normally have at least one adult male who leads the group’s travels and protections, sometimes along with other adult males, and a variety of females and youngsters. But last week, leading silverback Giraneza disappeared from his small group of two females and two infants, and has now been found several kilometers away and showing signs of illness, which is likely the reason he became separated from the group. The two mothers are clearly distressed, making hooting vocalizations and walking a lot, but are not within range of Giraneza at this time.

Concerns for the females

We are especially worried because these mothers each have an infant of just over 1 year old. We have assigned a tracker team to follow Giraneza separately, while another team follows the mothers and infants.

Gorilla infants are completely dependent on their mothers at this young age, and won’t start the weaning process until they are about 3-4 years old. Thus, the mothers are very busy carrying, caring for, and feeding the infants, including getting enough food for themselves to produce the energy and milk needed during this time. 

The reason this situation is so concerning is that infant gorillas are particularly susceptible to injuries, including potentially fatal ones, inflicted by unrelated males from outside the group.  One of the key roles of a silverback is to defend his group’s infants, and so the infants of these females, without an adult male, are at particularly high risk. The two mothers have even run into buffaloes in the forest since they’ve been without the silverback.

Gorilla motherhood isn’t easy

“Gorilla moms are simply amazing,” says Dr. Tara Stoinski, Ph.D., president and CEO/chief scientific officer of the Dian Fossey Gorilla Fund. “They are incredibly nurturing and each infant requires years of investment—roughly nine months of pregnancy plus three years of nursing—before it is fully weaned.

Raising an infant gorilla is not an easy task even under the best of circumstances. Infant mortality is high—generally a fourth of all infants die before their third birthday—and injuries from outside males play a significant role, Dr. Stoinski adds. “So it is no wonder we are seeing the females actively searching for Giraneza.”

Mother Pasika is 26 years old and has good experience raising offspring. Her current infant (named Mashami) was born in March 2016 and is her fourth offspring, three of whom are still living. Mother Kurinda is 14 years old and her current infant (named Nyampinga) is her third offspring, although the previous two did not survive.

Pasika and infant Mashami
Female Kurinda chestbeats

Studying the silverback’s behavior

Silverback Giraneza is 22 years old and formed his small group in 2015, after a variety of failed attempts, some years as a lone silverback. It is not clear whether he is the father of the two infants, since the mothers transferred to his group at a time when they could already have been pregnant. The leading silverback in their previous group died after being wounded in an interaction.

Several times in the past Giraneza has formed groups only to see the members leave him for other groups or having to battle with other silverbacks to gain females. Just last month a third female in his group transferred out to another group. But the situation this time is different, due to his possible illness, and will be closely monitored by Fossey Fund staff.

The Dian Fossey Gorilla Fund’s Karisoke Research Center, established by Dian Fossey in 1967, is the longest-running gorilla research project in the world. Yet, even with 50 years of gorilla data, there is still much to learn. The detailed data the Fossey Fund collects on the lives of individual gorillas like Giraneza, Pasika and Kurinda provides the scientific building blocks that help us understand gorilla life history, reproductive success, infant survivorship and thus, ultimately, their conservation.  With fewer than 880 individuals remaining, mountain gorillas are one of the world’s most-endangered animals and so this kind of close observation is of critical importance.   

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