Quick facts on fall bird migration

Some birds — rubythroated hummingbirds, orchard orioles and others — began heading south for the winter as early as July. But for most of Georgia’s Neotropical songbirds that nested here during spring and summer, September is when fall migration kicks into high gear.

Here’s a brief primer:

What is migration?

Among birds, it’s the annual, large-scale seasonal movement between summer breeding homes and non-breeding winter grounds.

Why do birds migrate in the fall?

There may be several reasons, but primary among them are to escape harsh winter weather in northern climes and to find reliable food sources. Of those, food reliability may be most important. A hummingbird, for instance, can withstand freezing temperatures as long as an adequate food supply is available.

What tells a bird it’s time to leave?

Probably a combination of things, including changes in day length, cooler temperatures, changes in food supplies and natural instinct. Migratory birds kept in cages may get restless during spring and fall, probably because of the natural urge to migrate.

What are Neotropical songbirds?

They are the birds that migrate to nesting areas in Georgia and elsewhere in North America during spring from winter grounds in tropical Central and South America and Caribbean islands. Georgia has 54 Neotropical species, including warblers, vireos, tanagers, swifts, cuckoos, swallows, thrushes, hummingbirds and others.

How far do birds migrate?

It depends on the species. Some may migrate only a few hundred miles — such as northern-nesting kinglets, which may migrate no farther than Georgia for the winter. Others, such as some warblers, may migrate thousands of miles as far as Peru and Brazil. Permanent residents like cardinals and bluebirds do not migrate.

How do birds find their way?

Bird navigation is poorly understood, but birds likely use cues from the sun, the stars and the Earth’s magnetic field and landmarks such as mountains and rivers to set their course.

In the sky: From David Dundee, Tellus Science Museum astronomer: The moon will be first quarter on Monday. Mercury and Venus are low in the west at dusk. Jupiter and Saturn are in the south at dark. Saturn will appear near the moon on Thursday; Jupiter will do so on Friday.

COURTESY OF TONY CASTRO/CREATIVE COMMONS The Kentucky warbler is one of 54 Neotropical songbird species that nested in Georgia during spring and summer and are now migrating to winter grounds as far south as Peru and Brazil in South America.