We are pleased that many of the issues that were relatively novel in behavioural biology when we wrote the first edition (1986) of this book have now passed into the mainstream of methodological thought. Nevertheless, we believe that the principles are worth reinforcing.

In this edition we have changed the structure so that greater prominence is given to the non-experimental aspects of behavioural biology. Some behavioural research simply involves carefully watching an animal to see what it does next. Performing an experiment may seem more ‘scientific’ than open-ended observation but the yield may be less. Moreover, worthwhile experimental research almost invariably needs to be preceded by careful observation. Knowledge of the normal behaviour of animals, preferably in their natural environment, is an invaluable precursor to experimental research.

We have also expanded the section on research design because, more than ever, good design can make such a difference to how big the sample must be, the interpretation of data and the time taken to prepare results for presentation or publication when the moment arrives. We have eliminated the further reading sections at the end of each chapter, but have given advice on further reading at appropriate places in the chapters. Each chapter now ends with a summary. We have taken out the annotated bibliography that formed such a large part of the reference section in the two previous editions (1986 and 1993) because we felt that such material was not essential to the main purpose of the book.