The migratory activity in the annual cycle of birds and its forms

The annual cycle of birds represents a system of genetically fixed and regular physiological states that determine the breeding behavior, growth and development, moult and migration. The annual cycle combines the photoperiodic control of seasonal events and the endogenous control of the others. There are three periods of the high locomotory activity in the avian annual cycle: postfledging (in young) or postnuptial (in adults) migration, postmoulting migration, and prenuptial migration. In these periods, the migratory activity may be different in different species and systematic groups. Four forms of migration are suggested for Palaearctic regions: long-distance (more properly, determined-distance) migration, nomadic migration, postfledging dispersal, and escape migration (or vagabondism). The direction and duration of the migratory activity is controlled by endogenous factors for the determined-distance migration. This form of movement is responsible for getting the birds to a certain place of the Earth for wintering and breeding. Cocoo, swift, swallows, some warblers, and flycatchers show the examples of such a form of migration. Obligatory directional movements are also characteristic of the nomadic migration. However, the total duration of the migration period comprises three following stages: obligatory movements and stages before and after obligatory movements related to search of places with abundant food. Therefore, the distance covered during such a movement, as well as wintering and breeding areas, vary from year to year. Siskins, redpolls, billfinches, and waxwinigs give examples of the nomadic migration. The obligatory period of migratory activity is absent in the annual cycle of birds with escape migration. Movements are stimulated by food failure, absence of favorable conditions for breeding or by some other external factors. As a rule, the high individual variability of migration distance and direction is observed in birds of the same population. Tits and crow may be an example of such a form of migration. Post-fledging dispersal should be considered as a special form of juvenile migration physiologically determined by the increased locomotory activity when young birds become independent.