Even in the warmest autumn, the leaves turn yellow and fall off. Migratory birds fly south. Many animals prepare for hibernation.

Even in the warmest autumn, the leaves turn yellow and fall off. Migratory birds fly south. Many animals prepare for hibernation. Why do these phenomena occur at the same time? What serves as a signal for leaf fall, birds’ flight, hibernation of animals?

1) The duration of daylight hours serves as a signal for leaf fall, bird migration, hibernation. 2) These phenomena – adaptations to the transfer of unfavorable winter conditions – are subordinate to the seasonal rhythm. 3) Seasonal rhythm – the body’s response to changes in the seasons, regulated by photoperiodism. Therefore, leaf fall, migration of birds, hibernation do not depend on temperature and other factors and occur at the same time.