Low air pressure areas in the fall trigger a southward migration. High air pressure areas in the spring encourage movement to the north. A lack of food in the fall and winter may also send birds toward areas where food supplies are more readily available. Birds migrate during the day or night. These birds navigate by sight and have few, if any, predators.
Songbirds migrate in the safety of darkness.
Their daylight hours are spent searching for food and resting for the next leg of their trip. Birds encounter many hazards during migration.