C. K. Catchpole is currently Professor of Animal Behaviour at Royal Holloway, University of London. He has written, broadcast and researched on many aspects of bird ecology and behaviour for more than thirty years and published over 100 books, articles and scientific papers. He has studied birds in many parts of the world and has been a visiting researcher at the Max-Planck-Institute for Ornithology in Germany and the California Academy of Sciences in the USA. P. J. B. Slater is Kennedy Professor of Natural History at the University of St Andrews. He is a former Editor of Animal Behaviour and of Advances in the Study of Behavior, and is a Past President of the Association for the Study of Animal Behaviour, which awarded him its medal in 1999. In 1991 he was elected to Fellowship of the Royal Society of Edinburgh. He is the author of around 150 scientific papers and several books, and has been studying acoustic communication, largely in birds, for thirty years.