The auks are marine birds widespread in the cooler parts of northern seas. Often regarded as the northern hemisphere's counterparts to penguins, they are accomplished underwater swimmers, able to dive to great depths. Among bird families, they exhibit an unusual degree of variability in their breeding sites, which range from old-growth, temperate forests to barren sea-cliffs and rocky outcrops among mountain glaciers. Chick development is equally variable: in some species chicks leave for the sea soon after hatching, while in others they grow to full size at the nest site. This diversity of behavior makes the auks an excellent subject for the study of adaptation. The authors, who have extensive field experience with auks, provide descriptions of the major features of the family and an engaging discussion of the adaptive significance of various traits. Part I contains general chapters on auk evolution, ecology, behavior, chick development, populations, and conservation. These chapters are illustrated with black-and-white drawings, summary graphs and tables. Part II follows with the twenty-three species accounts, giving comprehensive information on the birds in their natural state, including distribution maps. All species are illustrated in color, in superb plates by Ian Lewington especially commissioned for this volume. The Auks is part of Oxford's multi-volume Bird Families of the World, a new series of handbooks for professional scientists and amateur ornithologists. Each volume gives a comprehensive synthesis of current knowledge on one bird family or several related families; the complete series will be the definitive source for information on species of birds.