Although breeding may not occupy a majority of a bird's time it is certainly one of the most important times of its life. Certainly, no species could survive without it and there are several reasons why migration contributes to a successful breeding event. Southern latitudes provide considerably better winter weather than most of us have here in North America. And during our summer, Central America is extremely hot while the southern temperate and Antarctic area is cold with ice and snow covering much of it. Certainly not all, but many of the birds that remain north in the winter eat seeds which do remain available in winter.
Northern summers have very long days that provide many hours for gathering food.
Tropical days are only 12 hours long. Days in the north may reach 16 hours or more. It takes a great effort and a lot of time to gather enough food to feed three or four youngsters that will increase to 50 times their hatching weight in just 13 days. Northward migration expands the available nesting and food gathering area of the world . Many migrating species occupy totally different areas while some merely expand their range to the north in summer, with some individuals finding nesting space to the north and others remaining stationary.