Book excerpt: Although the 12 species representing three waterfowl tribes described in this volume are not closely related, they fortuitously provide an instructive example of adaptive evolutionary radiation within the much larger waterfowl lineage (the family Anatidae), especially as to their divergent morphologies, life histories, and social behaviors. The whistling-ducks (Dendrocygna), with three known North American species, are notable for their permanent pair-bonds, extended biparental family care, and strong social cohesion. In contrast, males of the five typical pochards of North American diving ducks (Aythya) establish monogamous pair-bonds that are maintained only long enough to assure that the female's eggs are fertilized. The endpoint of this behavioral gradient, promiscuity or polygyny, exists among at least some of the typical stifftails (Oxyura). Such diverse reproductive strategies have exerted powerful evolutionary influences on interspecies variations in sexual dimorphism, sexual behavior, anatomy, ecology, and other traits. This volume includes more than 63,000 words, plus some 200 maps, photos, drawings, and sketches, and nearly 650 literature citations. It is the last of five volumes that describe all 55 waterfowl species that have been historically documented in North America; collectively, the volumes total over 300,000 words, with nearly 3,000 literature citations, and more than 600 maps, photos, drawings, and sketches.