Many factor, the main ones are like to avoid extreme weather conditions or to go to a better environment condition. To find for new breeding grounds or food.
history of the migration: sentence:caused of people in need or forced to move employment. jobs. education. political/religious persecution. wars. overpopulation. better society. better facilities of...
Animals move from one place to another because of climate changes, the availability of food, or to ensure reproduction. Another reason for migration would perhaps be to complete a lifetime (for...