The correct word is “migrate.” Birds travel seasonally from one region to another, and this process is called migration.
“Immigrate” and “emigrate” refer specifically to the movement of humans into or out of a country, not animals following seasonal patterns.
Migration is an instinctive behavior that helps birds find food, breed, and survive harsh weather conditions.
Using the term “migrate” correctly highlights the natural, cyclical movement typical of many animal species, especially birds.
Therefore, when describing seasonal animal movement, “migrate” is the most accurate and appropriate term to use.