Question

Why do birds in cold climate migrate to warmer regions in winter?

Answer 1

because the birds need warm climate in winter so, they migrate to warmer region during winter

Answer 2

The birds from cold climate can migrate to warmer regions in search of foods and for the breeding purpose.  

EXPLANATION:

Most of the birds are depends on the nectar and the large insects for the food but these food may be available in the time of the winter season so the birds prefer to migrate from the cold climate to the warmer region in the winter season. Birds can also change their place to breed in a suitable condition.