Надо написать короткий топик на на тему "миграция животных".

Migrating animals (from Latin migrans.) - Regular movement of animal populations, in which individuals from one area to another habitat move, but then come back. Migrations are most common in birds (avian flights) and fish (eg, migration of Pacific salmon).
Migration can be divided into active (animals move themselves) and passive (animals are moved on the ice or water rushing). Active migration can be divided into time slots in which they occur:
ActiveSeasonal migrationDaily migrationPeriodic migration
As examples can be given seasonal movements of microscopic animals from the deep part of the lake in shallow water, associated with changes in water temperature, and the whale migration, which in the fall swim from polar regions in the subtropics, where hatch their young, and at the end of spring back into cold water .
Movement of animals caused by the necessity to change the environmental conditions or due to the passage of the development cycle.