Why do migrating birds bother to fly back north?

The primary reason that our feathered friends migrate South in the Fall, or North in the Spring, does not solely lie in the cold of winter, as most are well-equipped to survive in extreme temperatures, but instead lies with the upcoming shortage of food. Mother Nature endowed birds with an internal clock that warns them to get out-of-town, or to face possible starvation. Because birds can detect seasonal changes.