Young hummingbirds will look similar to a female, but as young males begin to mature in late summer look for a few random red iridescent feathers on the throat. And the young are very healthy looking. Their feathers are full and shiny whereas the parent birds look a little haggard. The parents have been through a lot and are now going through a molt to get ready for fall migration.
Only 20% of newly fledged hummingbirds live to be one year old. Once immature birds leave the nest they blunder about checking everything as they try to recognize the shapes and color patterns of blossoms or feeders that have nectar. This information is stored away in BB sized brains for the rest of their life. If they survive, they will continue to remember the exact location of gardens and feeders for years to come.
Immature hummingbirds also tend to be more vocal, calling out when distressed. And they have to learn a lot about social order. It's not unusual for more mature birds to use physical rebukes to punish young upstarts.
Finally the largest number of hummingbirds buzzing through our yards during late summer are immature birds that have only hatched recently. They can stay around mid-Michigan as late as October or November until all of a sudden they can't resist the urge to migrate south.
So keep those feeders full and clean! A hummingbirds' high metabolic rate requires them to refuel with nectar constantly while they search for bugs. They prefer flowers with a sugar concentration of 20 percent sucrose. This translates to a mixture of four parts water to one part white table sugar. Click HERE for more detailed nectar recipe instructions.
Source: Wild Birds Guides: Ruby-throated Hummingbird by Robert Sargent available at Wild Birds Unlimited