exist—and thereby evaluate the relative roles of extrinsic, intrinsic, deterministic, and stochastic causes for avian diversification.
Presumably, it was only a distant dream of mid-century participants in the Modern Synthesis that one day genetic analysis would come to dominate so completely the analysis of speciation in a clade such as birds. That genetics would be a useful tool in the analysis of speciation in model organisms had been evident since the early days of Drosophila genetics. Yet Mayr’s Systematics and the Origin of Species (1942), published 11 years before the discovery of the structure of DNA, was a treasure-trove of speciation stories not of logistically tractable species with easily sampled and manipulated populations; rather, this book focused on speciation stories from the distant South Pacific, on what were, even for ornithologists, virtually inaccessible taxa with ranges straddling some of the most remote and challenging habitats of the planet. The allure of the exotic continues for ornithologists: Mayr and Diamond have recently undertaken a complete taxonomic and biogeographic revision of the birds of the Solomon Islands (2001), and detailed molecular phylogeographic tests of several speciation stories in this assemblage are finally underway (Filardi, 2003; Filardi and Smith, 2005; Smith, 2003). Indeed, the role of molecular techniques introduced to ornithology with the first allozyme surveys of avian populations nearly 35 years ago has been primarily to inform the geography and timing of speciation, thereby emphasizing extrinsic aspects of the speciation process: species delimitation, allopatric speciation, ecological divergence, bottlenecks, and the role of the Pleistocene (Avise, 2000; Barrowclough, 1983). Those mechanisms of avian speciation described by Mayr in terms of internal factors—for example, speciation resulting from so-called “genetic revolutions” (Mayr, 1963)—were often vague and, in the case of genetic revolutions, have been largely discredited (Barton and Charlesworth, 1987).
In the last 10 years, however, there has been a renewed interest in the behavioral, cognitive, and even molecular mechanisms of speciation in birds. This renaissance, spearheaded largely by recent reviews by Price (Irwin and Price, 1999; Price, 1998, 2002; Price and Bouvier, 2002), builds in part on the ancient tradition of avian husbandry and domestication, and in part on theoretical models suggesting a role for diverse behavioral factors in bird speciation, including sexual selection, sexual imprinting, learning, reinforcement, and genetic incompatibilities. Although biogeographic analyses still largely support allopatric speciation models (Coyne and Price, 2000), recent years have also witnessed the first serious attempts to document sympatric speciation in birds (Grant and Grant, 1979;