Dismigration

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Dismigration or settlement dispersion is above all an ornithological technical term. This includes dispersal migrations of birds , in particular, but not exclusively, of young birds, which lead them away from their place of birth or from the place of the last brood . These migrations are an important factor in population ecology. Above all, they serve the purpose of habitat exploration and habitat expansion, the maintenance of population density and genetic diversification . Dismigration is an active migratory behavior that diffuses at will in the direction of distribution and that, in the narrower sense, is shown by single breeding bird species. In the case of colony breeders, the dismigration depends above all on the availability of suitable colony locations.

Dismigration leads to dispersion, to the best possible distribution of a bird species in suitable habitats. The dispersion is therefore the state after dismigration has taken place and not the process itself.

If the dispersal migration of a bird species is determined endogenously , the term dispersal is also used. If it is subject to exogenous influences, such as weather conditions or the availability of food, it is called spacing . In juvenile birds, dispersal and spacing often follow one another: First, the young bird moves away from its place of birth and only then selects its new habitat according to the criteria of habitat quality. Dismigration behavior differs from species to species as well as within a species and even within a population. Within populations, individual individuals can show a high degree of loyalty to the breeding site ( philopatry ), while others tend to have comparatively wide dismigrations. This behavioral polymorphism, which can be observed frequently, represents a special adaptation to a dynamic environment.

The distances of the dismigration flights are very different and are strongly related to the demands that the species makes on its habitat. The degree of species-specific territoriality also plays a not insignificant role. Depending on the species , the distance from the breeding site can be only a few 100 meters, but also a few 100 kilometers. In general, larger species show more dismigration flights than smaller ones.

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