Read the text and answer the question below. Many species of birds migrate long distances. In the Northern Hemisphere, birds fly north as the weather becomes warm in the spring and
south when the weather grows cool in the fall. Some migratory birds are called diurnal migrants because they migrate during the day when the
sun heats the air. The warm air rises, creating a lift that helps these birds fly at higher altitudes. Predators such as hawks and eagles hunt other
animals for their food and are diurnal migrants. By contrast, most song birds such as warblers and sparrows are called nocturnal migrants
because they migrate at night to evade these predators. Some nocturnal migrants fly long distances before landing in the morning to forage for
insects, fruit, or seeds in order to refuel for their next flight. Foraging birds may feed in an area for up to a week before setting off again under
the cover of darkness.
Question: What is the purpose of the text?