This book tells the story of the development of a new approach for predicting the impact on shorebirds of the many human activities that are carried out on estuaries and embayments such as shellfishing, recreation, building ports, sea -level rise and so forth. The approach is based on the behavior of individual birds and how they react to changes in their environment. It is an approach that does not require special biological knowledge to understand. The book describes how the fieldwork was carried out and how the eventual success of the project owed a great deal to good luck and to colleagues from all over the world. The book is partly aimed at amateur and professional biologists, ornithologists and naturalist interested in the ecology and behavior of shorebirds and in their conservation. It is also intended for people in government, professional organisations and NGO's along with environmental consultants and conservationists who are concerned with managing estuaries. The book provides an easy access to an approach that is being used by some authorities but of which other authorities may not yet be aware. The intention is for the book to be of interest also to students and lecturer in ecology and conservation. It describes a new approach to evaluating the impact of human activities on shorebirds that they might not otherwise encounter. The original research papers are scattered throughout scientific literature and it is sometimes difficult to see the whole picture, and to fully understand why the approach was adopted in the first place. The book should also give students considering a career in field research on birds an idea of what it can be like. Unlike most books on birds, this one not does claim comprehensively to summarise what is known about the breeding biology, migration, population dynamics, conservation requirements etc of a particular group of birds. Nor does it summarise the current state of knowledge about a topic, such as bird migration. Rather, it describes the origin and development of a new approach to providing the advice that nature managers require to make evidence-based decisions on how estuaries might be managed to retain their value to the huge numbers of migratory shorebirds that occur there, mainly during the non-breeding season. Now that the method has been developed, it is possible for the first time to forecast the impact of most changes in the way in which an estuary is managed or changed by a proposed development on what really matters: that is, on the chances of the birds surviving the non-breeding season in good enough condition to migrate successfully to their often distant breeding grounds. The need to carry out such research arose while forecasting the impact on shorebirds of the proposed construction over mudflats and sandflats of the Wash in east England of a huge fresh-water reservoir. But the approach itself was actually pioneered and tested from the mid-1970s onwards in a research programme on oystercatchers feeding on the mainly man-made mussel beds of the Exe estuary in Devon. The first half of the book describes this research programme. The next part describes how the approach was extended and used to investigate the impact on oystercatchers of alternative ways of harvesting cockles and mussels, not just on the Exe estuary but also the Burry Inlet and Menai straights in Wales and in the baie de Somme in France. The approach is now used to advise the authorities on how to harvest shellfish in a bird-friendly way in many parts of the UK. The remainder of the book describes how the approach was modified so it could be applied rapidly to any shorebird species eating any kind of invertebrate prey anywhere in the World. Simultaneously, it was adapted for herbivorous wildfowl and to populations occurring in many widely-separated places, such as intertidal flats and costal fields along the coast of northern Europe.