Territories and home ranges

At some time in the life cycle, most birds seem to space themselves by means of habitat selection and behavior. Within the home range, depending on time of year and functional need, many species of birds have a well-defined breeding or feeding territory that is defended by singing, calling, and/or aggressive chases; some waterbirds also defend stopover sites during migration and winter territories. The origins and advantages of such behavior has been discussed by many workers, and include resource protection, foraging efficiency, predator defense, population regulation, competitive advantage, and energy efficiency (Anderson and Titman 1992, Ashmole 1971, Orians 1971). Many waterbirds are highly social in breeding and feeding, and although territories may be clear-cut and violently defended, there is a wide range of territory size and behavior among wetland birds. While there is a positive relationship between body size and territory size in birds (Schoener 1968), it also seems to be dependent upon nesting and feeding strategies. Defense of territories that incorporate most life functions, such as mating, nesting, and feeding (see classification in Pettingill 1970), is most common among species that for reasons of food supply, water access, or nest cover restrict themselves to small but diverse patches and move little during the breeding period, e.g., some grebes and loons (Bergman and Derksen 1977), or coots (Gullion 1953). Species that nest colonially, such as egrets, herons, ibises, cormorants and pelicans, commonly defend only a small area of the tree, shrub, or marsh vegetation or substrate that is a mating site as well as nest site.