A lot of us think that baby birds grow up in a family that stays together and migrates south together. There are families of birds that stay together after the nesting season, but they are rare.
Most young birds are totally on their own soon after they leave the nest. In fact, in many bird families, the parents migrate south long before their youngsters do.
The best example of this is in the hummingbird family. The female raises her offspring until they are out of the nest and able to feed themselves. A few weeks later, she disappears. The youngsters are left alone to fatten up for their long migratory flight to a place in the tropics where they have never been before. They linger at the natal feeding grounds for several more weeks, sucking up as much nectar, sugar water and tiny insects as possible before heading south. How do they know when to leave, where to go, how to get there and when they have arrived? Herein lies one of the great mysteries of nature.
The same is true among juvenile ducks, warblers, vireos, flycatchers and thrushes. They are all deserted by their parents and left to find their way to some place in the South where there is food and habitat.
Juveniles of permanent residents, like chickadees, nuthatches, finches, and woodpeckers, are much better off. Though their parents no longer care for them, at least they are still in familiar surroundings.
--- George H. Harrison