Gorillas typically give birth to only one infant at a time. Gorilla Twin birth is a rare event in mountain gorillas. Even with the birth of twins, the survival for twins are very limited. The reasons for low survival rates of twins are not yet fully understood, but it is thought to be related to the difficulties in the care of the two babies. This is mainly because gorilla mothers are completely responsible for infant care at early birth stage and even despite the increased energetic demands of nursing twins, she will not allow other group members to hold or assist in any other way.
There are currently 8 and 4 documented cases of gorilla twining in Rwanda and Uganda respectively in the last 50 years. Because 50% of the Bwindi gorillas are wild unhabituated, there are several twin births that are not reported as they can’t be monitored in the wild unhabituated state. Trackers from Uganda Wildlife Authority have however witnessed at least 3 mothers from wild unhabituated gorillas with twins. This brings the total recorded twin births in Rwanda to 8 and 7 in Uganda. There are however no records of the surviving sets of twins in Uganda.
In Rwanda, the first set of twins were born in 1986 and only survived nine days, while those born in 2008 died the day they were born because of infanticide. In Uganda, the first recorded set of twins were born in 2004.
Susa A gorilla group is the first known group to have a set of surviving twins in the history of mountain gorillas. The birth of the twins occurred in May 2004 when Nyabitondore gave birth to two babies who were later named Impano and Byishimo (the male was called Byishimo meaning “joy” and the female Impano, meaning “gift”). Another twining occurred in the same group later in 2011 and they were named Impeta and Umudende, although Umudende passed on in 2015 (Impeta “a medal” to signify that the Susa group should be awarded a medal thanks to their status and Umudende, “an award of high value” to signify the same award for the Susa group). Hirwa group is known to have the second ever surviving twins named Isango Gakuru and Isango Gato born to Kabatwa.
One of the most recent case of twinning was in Rwanda’s Volcanoes National Park where Isaro, a 16-year-old adult female of Isabukuru group, gave birth to two babies. This highly welcome birth was recorded on 18th January 2016. It is unfortunate that only one of the twins is surviving. Again, in August 2016, Kalisimbi, an adult female in Amahoro group was spotted with newborn twin babies, but unfortunately the twins died the following day. The mother kept carrying both dead infants all night, but droped them the following days. The two babies (both females) died of traumatic injuries.
In Uganda, Nkuringo family is the first gorilla group to record the birth of gorilla ‘twins’ in Bwindi Impenetrable Forest National Park in December 2004. One of the twins however died shortly after birth as the mother could not take care of the two infants. The Nkuringo family welcomed a set of twin gorillas from mother Kwitonda, named Katungi and Muhozi. Unfortunately, Katungi died at the age of 1.5 years due to illness. Another twin birth occurred in 2008 in Nkuringo group. There are also records of twin births in Kyaguliro group.
One of biggest challenges of twin mothers in the first few weeks after the twins’ birth is keeping up with the group, as mothers usually use their arms to support infants until they are strong enough to grasp on tightly by themselves. Mothers with twins can be seen struggling to take care and feed both twins. The group members where twins are born have always been seen helping the mother care and transport the twins.
It is important to note that female gorillas become sexually active at approximately age 6 and then go through what is called ‘adolescent infertility’ for usually at least 2 years, during which time they will mate but will not become pregnant. The average age of first birth is approximately age 10 years (range 8-13 years). Gestation (pregnancy) length is 8.5 months. The typical interbirth interval (time between births of offspring that survive) is 4-5 years.