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.
Source: www.elpac.org
According to the text, what is one reason song birds migrate at night?
a.
to take advantage of rising air
b.
to avoid predators
c.
to navigate using the stars
d.
to escape the hot sun