Migration can help animals in many ways. Following a migrating food source or searching for an area that has a food supply when the current one is gone. Migration is also used for survival due to weather conditions. Some animals cannot tolerate extreme heat or extreme cold and therefore must seek more suitable environments depending on the time of the year. Animals can also migrate to a location they believe is best for young and seek a mate for reproduction there. I'm sure there are more reasons but that's the general idea anyways.