Territorial Behavior and Population Regulation in Birds

A close relationship between territorial behavior and population regulation in birds was claimed by Howard (1920) in his classic essay on territoriality and has been emphasized by both earlier and more recent authors (see Wynne-Edwards, 1962). At present, opinions on this matter vary considerably; but there seems to be widespread entertainment, and in some circles acceptance, of the idea that territorial behavior sig nificantly limits many avian populations. Frequently appended is the theory that territoriality has evolved because of this effect through a process which has been called “group selection” but which might better be referred to as “interpopulation or interdemic selection” (Brown, 1966). These ideas apparently were first fully developed by Kalela (1954:2, 18, 41) and have recently been elaborated in the ecological literature by WynneEdwards (1962, 1963, and elsewhere) and in the popular press by Lorenz (1966:31). The role of territorial behavior in population regulation is now regularly covered in college textbooks of ecology and behavior (e.g. Andrewartha and Birch, 1954:490; Odum, 1959:222; Kendeigh, 1961:222; Macfadyen, 1963:264; Davis, 1%6:68; Smith, 1966:372; MacArthur and Connell, 1966:139; Etkin, 1967:32), despite the claims of some ecologists (e. g. Lack, 1954, 1966) that it is of relatively little importance. Surprisingly, the facts necessary for an evaluation of the role of territorial behavior in population regulation have received relatively little critical attention except in parts of works with a more general orientation. As a result the various ways in which territorial behavior may affect a population do not appear to have been as clearly distinguished and as thoroughly studied as their presumed importance might suggest. This review attempts to identify and evaluate the effects of territorial behavior on population density by examining the evidence from the best studied territorial species. The approach employed, which stresses comparative population dynamics, also enables new insight into the evolution of certain perplexing types of social organization and behavior in birds. Consideration will be limited mainly to species in which the same territory is used for feeding, mating, and nesting, Nice’ s (1941, 1943) Type A territories, since these species offer the most persuasive evidence for the population limiting effects of territorial behavior.