May 16, 2012
Silverback Fathers Can be Motherly Too
The highly social nature of the gorilla species is world-renowned, thanks to the groundbreaking mountain gorilla behavioral study that Dian Fossey, Ph.D., began in 1967. It may in fact be what makes these large primates so endearing to humans. By far the most exemplary social relationship is the mother/offspring bond. A gorilla infant is heavily dependent on its mother for the first several years of life, needing nourishment, warmth and constant protection from the elements.
Less commonly showcased is the father/offspring bond that can occur when the mother prematurely leaves the group through either a transfer or death. In this circumstance, the bond can become unusually strong, as the silverback may step in as the infant’s surrogate mother. If an infant loses
its mother within the first or second year of life, the chance of survival is extremely low. However, if the youngster has graduated from infant to juvenile (around the age of 3) by the time of separation, it has a higher chance of survival. In this situation, researchers have observed that the youngsters tend to forge a bond with a silverback rather than with other females in the group. This creates a special relationship between silverbacks and their offspring and there have been many memorable pairs over the course of the mountain gorilla monitoring conducted by the Fossey Fund’s Karisoke Research Center.
Inshuti and Akarusho
Recently, one such unique pairing between silverback and infant emerged within the Karisoke research groups. The field staff has seen the youngest infant to date survive abandonment by his mother, thanks to the surrogacy of his group’s dominant silverback, Inshuti. In February 2012, Inshuti’s group underwent a series of dramatic interactions with lone silverbacks, leading to two adult females leaving to join silverback Giraneza. Somewhat unexpectedly, Akarusho’s young mother, 12-year-old Taraja, chose to leave her 2.8-year-old youngster behind to follow the newcomer. Wisely, Akarusho chose not to pursue his mother (which would have put him at a greater risk of infanticide by the new silverback), but chose instead to go back to Inshuti. The youngster spent a night alone in the forest when he was unable to find the injured silverback, but the following morning Karisoke trackers witnessed their reunion, filled with desperate squeaks and squeals from Akarusho. From that point on, Akarusho has not strayed far from his massive guardian.
Inshuti, injured and stressed, traveled many kilometers during the weeks following the interactions, in an attempt to avoid any further aggression from lone silverbacks. He has led what is left of his little group well outside of its usual home range and they are now high up on the slopes of Mount Karisimbi. The cold, rainy weather at this altitude and the constant travel would be a challenge for any youngster, and there is no question that Akarusho would not have survived if Inshuti had not taken such a keen interest. Inshuti builds deep, thick nests to ward off the inclement weather, and the youngster sleeps with him, warm and safe, snuggled close to Inshuti’s massive body. The pair feed together, groom one another and act as a mother and her offspring would.
Kirahure and Rugira
In June 2011, 3.2-year-old Rugira was left behind when her mother Muganga transferred to Isabukuru’s group. Fortunately, this outgoing youngster bonded immediately with dominant silverback Kirahure (who had recently become the dominant silverback of Kuryama’s group). Rugira is lucky in that there are five other youngsters in the group who provide enrichment and entertainment for her. These relationships have helped to bolster her early independence and ease the trauma of losing her mother so early in life. They may have also led to an unusually early display of mothering tendencies in Rugira. She is often seen stumbling around with young Dukore on her back (an infant not too much younger than she is), attempting to carry him around as a mother would her own offspring.
Right after her mother’s transfer, the field staff reported that Rugira was visibly depressed and her playful behavior had ceased. She chose instead to spend her time quietly following dominant silverback Kirahure around. The silverback responded immediately to the infant in need and began to share his night nest with her, protectively staying close to her during the day. But if Akarusho and Inshuti exhibit more of a parent/offspring dynamic, Rugira and Kirahure appear to be more like good friends. Rugira’s paternity is not certain and Kuryama – not Kirahure – was the dominant silverback at the time of her conception, though females tend to copulate with multiple silverbacks while they are pregnant. Some suspect that this may be a ruse to confuse their offspring’s paternity and ensure protection from potential infanticide. Whether Kirahure is in fact Rugira’s father or not, one thing is for certain: If the big male had not stepped in as Rugira’s surrogate mother, filling her need for warmth and protection, the lively young gorilla might not have survived.
Titus and Ihumure
Perhaps the most memorable pairing occurred near the end of the legendary silverback Titus’ life. Born in 1974, Titus was named by Dian Fossey’s research assistant Kelly Stewart. At the tender age of 4, poachers killed Titus’ father Uncle Bert, his uncle Digit and his younger brother. Shortly after, his mother and older sister fled the group when silverback Beetsme killed Titus’ infant sister. Titus was left alone save for a few unrelated males in the group. Tiger, an 11-year-old blackback in the group, took on maternal responsibilities for the young Titus, helping to ensure his survival in the world.
Titus showed an early inclination to mother orphaned youngsters, and during the beginning of his leadership took on infants Taraja and Turakora after their mothers were gone. Some 30 years later, another young infant was left motherless in his group. Three-year-old Ihumure’s mother, Bukima, left Titus’ group to join silverback Isabukuru in March 2009. Titus, already well known for his gentle nature, immediately stepped in as his surrogate mother. Veronica Vecellio, Karisoke’s gorilla program coordinator, reflects that Ihumure “was so insecure, such a small little guy. He was incredibly dependent on Titus and Titus took such good care of him.” When Titus died on Sept. 14, just seven months after their special bond had been forged, the youngster refused to leave the deceased silverback’s body, appearing depressed and frequently crying out. Just a few days later, on Sept. 17, Ihumure died also.
There have been many other cases of silverbacks taking on the maternal duties for vulnerable infants. Dominant silverback Bwenge currently has two infants, Akaramata and Ntaribi (both of whom lost their mothers in September 2011), sleeping in his night nest and depending on him for comfort and protection. When Pablo’s group split in 2006, three infants were separated from their mothers. Two of the infants died soon after, but the oldest of the three, Agahozo, latched onto the third-ranking silverback of the group, Umuruva. In 1978, Dian Fossey had observed 4-year-old Pablo nesting with dominant silverback Beethoven after his mother, Liza, transferred out of the group. Two years later, 3-year-old Shinda was left alone when his mother Marchessa died of natural causes. Once again, Beethoven took on the maternal role for the youngster, ensuring the survival of what would one day be an extremely successful, legendary dominant silverback.
Jessica Burbridge, Field Communications Officer