(noun) The periodic seasonal movement of birds from one geographic region to another, typically coinciding with available food supplies or breeding seasons. Birds may travel hundreds or thousands of miles during migration, depending on the species and the areas they prefer for nesting habitat and wintering grounds, and it may take several weeks to make the entire journey. Some species travel separately according to gender, usually with male birds migrating earlier than females in order to secure territories or begin nest-building activities to attract mates.
Migration periods during the spring and fall are considered prime birding times, since they give birders the opportunity to see many transient species in between their established habitats. Because birds also use regular corridors for migration flights, it can be easy to find a large number of diverse species in a relatively small range during migration.