One can choose a point instead and measure the radial distances of the animals detected. It is very appropriate that the leading exponents in this field have come together to produce an authoritative description on 'how to do it'. They bring with them many years of experience in this research area. This book is a must for all those involved in estimating animal abundance as the methods can be used for such a wide variety of animal species including birds and marine mammals. The methods also apply to clusters of animals such as schools of dolphins and to animal signs. The beauty of such methods lies in the fact that not every animal has to be seen when a population is investigated. At the heart of the methodology is a 'detectability' function which is estimated in some robust fashion from the distances to the animals actually seen. Many species are not always visible and may be detected by the sounds they make or by being flushed out into the open. Clearly animals can have widely different behaviour patterns so that different models will be needed for different situations. This book provides a tool box of such methods with a computer package which helps the researcher to select the right tool for each occasion. The authors have a reputation for being very thorough and, typically, they endeavour to cover every conceivable situation that might be encountered in the field.