Chapter 2 - Social Systems and Status

Abstract

This chapter describes the habitat and the regulation of population density of birds. In conjunction with dominance behavior, spatial variation in habitat is involved in the regulation of bird numbers. The central idea is based on two generally accepted tenets. First, for any species, habitat varies in quality from place to place, which is beneficial in terms of survival and reproduction. Second, as numbers rise, a good habitat is occupied first and is preferred to a poorer habitat. Such a pattern depends on individuals distinguishing and preferring a good habitat, and beyond a certain level of occupation, a deterring settlement by further individuals, who then move into poorer habitats. If these conditions hold, it follows that, as total numbers rise, an increasing proportion of individuals are pushed down the habitat gradient where their survival or breeding success is reduced. Some individuals may be excluded from the nesting habitat altogether, and accumulate as a nonbreeding contingent or die. As a result of these processes, the mean per capita performance (survival or reproduction) for the population as a whole declines progressively in a density-dependent manner.