These two books represent a synthesis and critical evaluation of studies conducted on bird communities, or sets of bird species that occur together. Drawing from studies conducted throughout the world, they review in detail what is known about the patterns of organization of such communities and the factors, such as competition, predation, past history, climate, habitat or disturbance that may determine these patterns. In Volume 1, the author considers why the avian community ecologists ask the questions they do, and how they have proceeded to answer them. The questions have generally involved both "what" (pattern) and "why" (process) components. Most of the volume is devoted to a critical evaluation of the patterns of bird communities. In Volume 2, the author considers how community organization patterns have been explained in terms of causal processes, how the operation of those processes has been determined, and how the patterns and our efforts to discern and understand them are influenced by the complexity and variability of natural environments.