When do hummingbirds migrate south?

It's not the lack of food that tells a hummingbird when to go south. It's the bird's internal biological calendar, or circannual rhythms. As the time of migration approaches, the hummingbird starts to pack on fat, which will fuel its journey. And then it gets an overwhelming urge to migrate. read more

The initial urge is triggered by the shortening length of sunlight as autumn approaches, and has nothing to do with temperature or the availability of food; in fact, hummingbirds migrate south at the time of greatest food abundance. read more

When Hummingbirds Migrate. Several factors affect hummingbird migration and when exactly these small birds set forth on their long journeys. The most important factor that determines the timing of hummingbird migration is daylight: the amount of daylight and the angle of the sun relative to the bird's location. read more