Earlier naturalists formed the impression that bird numbers remained more or less stable through time. In the years since these words were written, however, changes have occurred in the landscapes of the British Isles and in the seas around our coasts, causing bird populations to fluctuate in an unprecedented way. In Ian Newton's latest New Naturalist volume, he explores bird populations and why their numbers vary in the way they do, from year to year or from place to place. He addresses the various factors that we know limit bird numbers – food supplies and other resources, competitors, predators, parasites and pathogens, and various human impacts. The combination of a rapidly expanding human population, a predominantly utilitarian attitude to land, central government policy on land use, and increasing mechanisation have combined to promote more massive changes in land use – and hence in bird habitats – in recent decades than at any comparable period previously. These developments have in turn brought huge changes in bird populations, as some species dependent on the old landscapes declined, and others benefiting from the changes increased. Over the same period, changing public attitudes to wildlife, protective legislation and a growing network of nature reserves allowed previously scarce bird species to recover from past onslaughts, while climate warming has promoted further changes. In this seminal new work, Ian Newton sets out to explain why different bird species are distributed in the numbers that they are, and have changed over the years in the way that they have. He emphasises the factors that influence bird numbers, rather than the numbers themselves, thus providing a much-needed overview which is necessary if we are to successfully manage bird populations, whether for conservation reasons, for sustainable hunting or for crop protection. The continued monitoring of bird numbers can also alert us to impending environmental problems. In addition, the regular watching and study of birds now provides a source of recreation and pleasure for very large numbers of people, who would find a world with fewer birds a poorer place.