Geese fly south in the winter to find food and nesting areas. Geese, like most birds, migrate to where resources are more abundant, which is often climate related.
When the weather begins to turn cold in northern areas, food becomes scarcer. As the population of insects and other food sources begin to decrease, geese naturally begin to move south. Another reason for migration is simply to escape the cold. When temperatures reach freezing, some types of birds cannot adapt the extreme temperatures. Some geese will travel thousands of miles when winter begins to set in. When the weather begins to warm as winter ends, the geese will return to their non-breeding grounds. They commonly only breed in warm months in the south.