In North America, hummingbirds begin migrating south in late August or mid-September. A few hummingbirds may begin migrating south as early as July. Hummingbirds that travel very long distances between their summer and winter feeding grounds start migrating earlier than other birds.
Male birds and mature birds tend to leave earlier than females and immature birds. Male birds leave a few days early so they can set up territories before the females arrive. Immature birds need to grow and consume more food before they begin on their long migration.
Unlike many migratory birds, hummingbirds do not travel in flocks. They do, however, travel very long distances and often take several months twice a year moving between their winter and summer homes.