the faculty of animals to select the direction of their movement during regular seasonal migrations to winter or spawning grounds. Bionavigation is made possible by the ability of an animal to orient itself in the environment with the help of sensory organs and instincts, or reactions reinforced by heredity. The importance of instinct is especially great in cases in which young birds who have never flown south for the winter undertake a migration. Besides birds, certain mammals which undertake long-distance seasonal migrations (for example, reindeer, fur seals, and whales) and also certain reptiles (for example, turtles) have a striking capacity for bionavigation. The interaction between animals in the migrating group plays a large role in the selection of the correct direction; for this reason, migrations of birds, for example, are usually carried out in flocks. The mechanisms of bionavigation are extremely varied (including navigation by the stars and by terrestrial reference points) and have not yet been sufficiently studied.