This paper presents a descriptive summary of the significant events which took place during a change in leadership of the Jersey Wildlife Preservation Trust's group of western lowland gorillas Gorilla g. gorilla. Following the death of the founder male in 1992, the group experienced a partial breakdown of its social structure. This was temporarily rectified under female leadership, prior to the introduction of a new male in 1993. The integration of the blackbacked male into an established breeding group, although initially problematic, influenced change within the female hierarchy, and subsequently led to the siring of a male infant from the youngest female. Whilst certain social relationships with the maturing male improved, others deteriorated, to the extent that the removal by transfer of two sexually mature females became necessary. Problems incurred at that time, both behavioural and medical, are described. Despite a marked improvement in group compatibility, the level of sexual activity among higher ranking females remained poor, and consequently a reproductive research project was initiated to investigate this problem. Details of the latter are given, along with observations on change in behavioural response to the new male, management strategies, maturation, dominance related behaviour, female transfer, sexual behaviour and oestrous cyclicity.
