They fly to find better food supplies (and better weather).
When birds fly South for the winter it is called migration.
The main reason that birds fly south in the winter is because they can't stay in a cold place so they fly south to a warmer place during the winter.
Monarch Butterflies. They fly south for the winter like birds do.
migration
migration
Migration
they are migrating to a certain place. (next time find out yourself)
It's warm
They don't stay when it is snowing. Hasn't anybody learned that birds fly south in the winter?
No. Only some species are migratory.
Instinct
because it is cold