A new gorilla family

After the death of 2 gorillas from our family group in 2013, it had been reduced from 5 to only 3 individuals: an adult female and 2 juveniles.
The western lowland gorilla (Gorilla gorilla gorilla) EEP (European Breeding Program) of which we are part recommended us to try to introduce Nyuki, one of the 2 silverbacks hosted on the second gorilla island of our great ape exhibit. But serious concern remained about a high risk of infanticide with two juveniles aged under 5 years old within the group.
In the wild indeed, when an adult male takes control of a group including infants he had no probability of siring, he can then kill them if they are aged under 3 (corresponding to the breast-feeding period). Used by males as a reproduction strategy to increase their reproductive success, infanticide leads to the onset of oestrous in the mother who will be ready for a new pregnancy, allowing the new male to sire offspring.
Introducing a new silverback in a group with juveniles represents the same risk in captivity. An additional issue with Nyuki is that he had been hand-raised and even if he spent the majority of his life with other gorillas (essentially males), his early life was spent in close contact with humans until his size and weight eventually make it unsafe for people. His social skills are thus reduced when compared to those of an individual raised by his mother within a family group gathering several individuals of all age with whom he can acquire all the mechanisms that will help him to be a well-balanced and experienced gorilla in adulthood.
Nyuki's introduction however had an advantage: trying a introduction that looked complicated with an animal born and who spent his all life at La Palmyre Zoo and whose personality was perfectly know by the keepers in charge of the gorillas...
So last year we followed the EEP recommendation and we transferred Nyuki close to the small family group so that all can progressively get to know each other in protected contact, meaning through a wire mesh that was preventing any attempt of physical aggression. The first contacts between the animals were encouraging and we were thinking about proceeding to the full introduction after the summer. However the EEP asked us to wait for the youngest member of the group to be at least 5 years so we decided to postpone the introduction to early 2015.
There was a big concern about the introduction from the team who had been strongly affected by the loss of a gorilla in the past few months. On "G-day", the opening of the hatches was attended by 2 veterinarians, the head-keeper and 3 keepers, all staying at different locations of the enclosure in order to intervene quickly in case of emergency.
The very first contact between the 4 individuals went quite well despite several displays, sideways running and calls which sometimes lead us to hold our breath!
Nyuki never displayed any aggressive behaviour while the 3 other individuals stood together. After 30 minutes, we decided to stop the contact as the pressure on Nyuki was quite high and we felt he was started to be tired.
The following days, we prioritized 1 to 1 contacts, either between Nyuki and our adult female, either between Nyuki and our juvenile male, whereas the 2 remaining gorillas were kept in the night cages.
Seeing that the situation was improving slowly, we put all the individuals together again and since then they all seem to get along well! Only 15 days after we started the whole process, we even observed playing sessions between Nyuki and the two youngsters, a nice and exciting moment for the whole team!
Even if all the tensions haven't disappeared yet, the evolution of the group is very encouraging. Nyuki doesn't react aggressively and handles this new situation without undue stress. As for the three other members of the group, they seem to adapt quite well to change, and are very curious about their impressive new leader.
The group will obviously remain under close monitoring. Next step: getting out on the island as soon as the weather will allow it.