Dispersal, defined as a linear spreading movement of individuals away from others of the population is a fundamental characteristic of organisms in nature. Dispersal is a central concept in ecological, behavioral and evolutionary studies, driven by several forces such as avoidance of inbreeding depression, density-dependent competition and the need to change breeding locations. By effective dispersal, organisms can enlarge their geographic range, and adjust the dynamic, sex ratio and genetic structure of a population. Birds are one of the groups that are studied intensively by human beings. Due to their diurnal habits, diverse life history strategies and complex movement, birds are also ideal models with which to study dispersal behaviors. Such studies on avian species represent a new frontier of ornithological research.
Dispersal is distinguished between natal dispersal and breeding dispersal. The former refers to the movement between the natal area and the first breeding site. Breeding dispersal is the movement between two successive territories. The main objective of avian dispersal research is to obtain the proximate and ultimate perspectives in a diversity of bird species. Certain topics of avian dispersal including sex-biased, asymmetric dispersal caused by differences in body conditions, dispersal processes, habitat selection and long distance dispersal are discussed here. To collect data of parameters of dispersal like distance and rate, it is sensible to mark individuals. Bird-banding or marking, radio-telemetry and genetic markers are useful tools widely applied in many studies. Moreover, satellite-tracking, stable isotope analysis and hormone examination are methodologies currently underway.
A number of empirical studies on avian dispersal have been published in recent years, proving it to be an active field in ornithology. The challenges that surround theories and methodologies impel scientists to continue their studies by following three aspects: (1) furthering methodological advances, (2) strengthening theoretical research, and (3) applying research into the conservation efforts for threatened birds and the management of their habitats.