Despite its great size, and colourful secondary sexual adornments, the behavioural biology of the mandrill (Mandrillus sphinx) remained shrouded in mystery until comparatively recently. It has given me much pleasure to study the behaviour and reproductive biology of mandrills in Gabon, and to supervise a number of research students who have helped to advance those studies. Indeed, I am indebted to a number of people who made the writing of this book possible. The late Dr Georges Roelants invited me to work at the International Medical Research Centre (CIRMF) in Gabon, and to direct research at its Primate Centre between the years 1989 and 1992. Dr Jean Wickings carried out all the genetic studies and hormone assay work on the mandrills during those years; these contributions were of vital importance. Two research students from the University of Zurich, Thomas Bossi (co-supervised with Professor Bob Martin) and Edi Frei (co-supervised with the late Professor Hans Kummer), helped to study the sexual behaviour and social organization of the mandrill. In later years, after I had returned to the UK to work at the Sub-Department of Animal Behaviour (University of Cambridge), Joanna Setchell joined our group as a PhD student, in order to research the socio-sexual development of male mandrills. After successfully completing her PhD, Jo Setchell continued to work on the mandrill groups at the CIRMF; her research publications, and those of her colleagues, have been of immense value to me.

The drill (Mandrillus leucophaeus) is even less well studied than the mandrill, but it is impossible to understand the evolutionary history of the genus Mandrillus without considering both these species. Thus, during six years spent in the USA, as Director of Conservation and Science for the Zoological Society of San Diego, I took the opportunity to initiate fieldwork on drills in Cameroon. In this regard, I owe a special debt of gratitude to Dr Bethan Morgan for her tireless efforts to gather data on free-ranging drills, and to Chris Wild who managed field operations in Cameroon from 2000 to 2005.