Gorilla Journal 34, June 2007

Cases of Twin Births in Three Gorilla Groups in Kahuzi-Biega

The gorilla subspecies Gorilla beringei graueri is endemic to the eastern Democratic Republic of the Congo, including the Kahuzi-Biega National Park, the Maiko National Park and the Itombwe Forest. In the early 1970s, two gorilla groups were tracked daily in the Kahuzi-Biega National Park for tourism, those of Casimir and Mushamuka, and tracking of gorilla groups has continued, whenever possible, since then. The genealogies of individuals from these groups have been documented. Trackers and guides as well as a few researchers had the opportunity to witness many different occurrences in the course of this daily tracking.
Amongst many births recorded, twins births were witnessed in the gorilla groups Maheshe, Mufanzala and Chimanuka over the three decades of the park's existence. Two sets of twins were born, to two different females, in the group led by the silverback Chimanuka, and two other sets were born in the groups Maheshe and Mufanzala (see also Iyomi & Schuler 2005).

The Maheshe Group
The late Maheshe (1960-1993), the son of Casimir (1924?-1975), had led a few members of his father's group since the late 1970s and early 1980s. In his group, many single babies were born and recorded, with more females than males. It was in Maheshe's group that the first case of twins was recorded. As nearly all the daily activities by the gorillas in the tourist sector (Mt. Bugulumiza and surroundings) were recorded by us, many copulations between the silverback Maheshe and one known female were witnessed in the period of mid-June 1988; they ceased toward the end of the year.
In July 1989, during an episode of Myrianthus holstii fruit harvesting by the gorillas, we witnessed the female carrying twin babies aged two days. They were carried ventrally by their mother, one on each side, and suckled from one breast each. The sex of the babies was discovered when the mother moved each of them once to collect food, or in grooming them during the siesta. They were both males.
When we named the twins, this meant also that the mother would be named. As is the custom in the Bushi territory in which the Bugulumiza mountain is located, a twin mother is called Mo-twi ("mother of twins") automatically; the twin which suckled at the right breast was called Jumaa and the twin which suckled the left breast was named Posho (both names indicate a week of the month), as they were born in the beginning of July.
The suckling and the health state of both twins was good and Mo-twi, the mother, took good care of them including their social integration in the family. Maheshe seemed to be very tolerant towards Mo-twi, and she appeared to be the top-ranking female of the group; it was she who was allowed to sit next to Maheshe, and she was seen most of the time grooming his hair during the siesta period. She always travelled next to him. If there was favourite food, like the wild banana tree Ensete ventricosum, we observed Maheshe eat first and Mo-twi next, before any other individuals of the group were allowed to eat.

Death of the Father, the Mother and the Twins...
According to our daily long-term observations, none of these four individuals, or any of the other members of the group, died naturally. Posho was squashed by the silverback Nindja during an interaction between him and Maheshe in September 1989, two months after his birth. Mo-twi was involved in the fight, trying to help Maheshe while carrying the twins ventrally, and unfortunately Posho received a trauma and was sick for a few days before he died. We observed the mother carrying both babies, the dead Posho and the living Jumaa. During the displacement of the group, Jumaa was carried on the chest and Posho in the hand of the mother. Mo-twi was mostly upright, and during feeding, she always placed the dead twin on the ground and fed with one hand until the group left; she would do this until Posho's body decomposed.
Maheshe himself was slaughtered and his head cut off by Pygmies to sell as a trophy on November 3rd, 1993 (Kahekwa 2005). Mo-twi, who later was re-named Mugoli (queen), took over leadership of Maheshe's group for over 8 months; it was the first time, in our experience, or to our knowledge, that a female had led a group after the death of the leading male.
During the war that has raged in the Great Lakes region since 1990, when tourism in Kahuzi-Biega National Park was suspended, the new male Lambchop from the Mushamuka family took over this group. Mo-twi copulated with Lambchop many times and had a new baby called Lwasi (leaf) in 1995. Lambchop, a son of Mushamuka, was then renamed and called Maheshe 2 by the authorities. This custom of changing the names can be confusing for anyone trying to track the data and origin of the individuals.
It was only after September 1999 that we were able to search for Lambchop's group in its territory, and missed all the members. We concluded that many of them were victims of slaughtering for bushmeat, because we came across three different campfires and found gorilla skulls and hair thrown around. Thus, Lambchop, Mo-twi, Jumaa and other members were consumed for their meat. At that time we found hardly any fresh gorilla nests or fresh paths.

Second Twin Birth: Mufanzala Group
During this period of intense human pressure on the natural resources of the Kahuzi-Biega National Park, which caused the death of almost half of the gorillas in the highland sector and the encroachment of their habitat in 1997 to 1999 (Kahekwa 2005), the gorilla groups habituated to human presence were much more vulnerable than the unhabituated groups. The Mubalala (traveller) group and other groups were slaughtered for bushmeat and possibly for live babies. Only very few members of this group escaped and moved for some time within their area until a wild silverback moved in; this new silverback was finally joined by the few surviving members and the new group occupied the area of the late Mubalala group.
This silverback was not easy to approach; he charged us from a distance and ran away every time. Only two of the rescued group members glanced at us occasionally. The trackers named the wild silverback Mufanzala (a hungry person); this was the name of a gorilla tracker who had worked in the PNKB since the early 1970s.
Gorillas who had lost their family structures were scattered everywhere, seeking other males or females for building up new groups. The silverback Mufanzala integrated several females and formed his own group, which was monitored every day, and at the end of 1999/beginning of 2000 the trackers and ourselves discovered a twin birth in this group; the twins, who were already almost 6 months old, were carried by a female used to people. She carried the twins ventrally and we only had a chance to see them briefly once or twice a month as the silverback would not tolerate our presence and usually led his group to hide from us when we would come. As a result, the sex of the twins remained unknown to us. Both twins are still alive and are now juvenile.
The discovery of the twins increased the count of the Mufanzala family from 12 to 14 members: 1 silverback, 8 adult females, 3 subadults, 2 infants. The absence of blackbacks and juveniles was remarkable.

Two Sets of Twins in the Chimanuka Group
The now famous silverback Chimanuka is a son of the late Maheshe and a grandson of Casimir, the first silverback whose family was visited by tourists in the early 1970s. Chimanuka was born in Maheshe's group in 1986 to a female called Cheko. His infant name was Soso (chicken in the Lingala language). He grew up in this family to maturity; as Maheshe did not tolerate the presence of his sons when they tried to mate with the females in the group, Chimanuka was forced to emigrate at the age of 8 years and to live a single life for years. It was remarkable that the males who had been chased from their paternal group did not move far away to establish their own home ranges; Chimanuka travelled in the surroundings of his father Maheshe's area. We found his paths and nests when we visited the groups Maheshe and Mushamuka.
For a long time after the slaughtering of many gorilla families for bushmeat (Kahekwa 2005), there were no gorilla groups habituated to people in the Mt. Bugulumiza sector. Finally we encountered narrow paths and two gorilla nests in the sector which formerly had been occupied by Casimir, Maheshe, Mushamuka and Nindja.
From September to October 2002, the first interactions between Chimanuka (Soso) and Mugaruka (Kaboko) occurred in the bamboo forest where the gorillas were consuming the new shoots. A few females transferred from Mugaruka to Chimanuka.
At the end of December 2002/beginning of January 2003, Chimanuka and Muhindo had their first offspring called Bonane (happy new year).
Chimanuka was responsible for the first recorded cases of infanticide in the Kahuzi-Biega National Park, although the gorillas had been observed for over 30 years (Yamagiwa & Kahekwa 2004). He killed 3 babies of different females who had transferred to him from Mugaruka's group. All the infants were males that were carried by their mothers.
Chimanuka took over Mugaruka's group and home range - almost 90% of the females and 90% of the area that Mugaruka had occupied. Matings between Chimanuka and the females that had transferred from Mugaruka were observed. From 2003 to 2005 7 births including 2 sets of twins occurred in this group. The two twin sets were delivered by two different females.

Other Births in the Chimanuka Group
After the transfers of most individuals from the Mugaruka group to the Chimanuka group, guides and trackers were not able to identify which females were mothers of twins or mothers of single babies. After multiple interactions between Chimanuka and other units as well as new births, the group increased to 26 members between 2003 and 2005. In 2005, the Chimanuka family consisted of 1 silverback, 15 adult females and 10 youngsters.

John Kahekwa

John Kahekwa has been working at the Kahuzi-Biega National Park since 1983. He habituated gorilla groups and took part in scientific studies until 2003. He founded the Pole Pole Foundation, which has been cooperating with the population around the park since 1992, as a new way to fight poaching.

References
Iyomi Iyatshi, B. & Schuler, C. (2005) Twin boom in eastern gorillas. Gorilla Journal 30, 9-10
Kahekwa, J. (2005) Dangers to Kahuzi-Biega and POPOF's Artisan Program. Gorilla Journal 30, 5-7
Yamagiwa, J. & Kahekwa, J. (2004) First observations of infanticides by a silverback in Kahuzi-Biega. Gorilla Journal 29, 6-9

Kahuzi-Biega overview

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