In this group of birds, the two on the left still have the brown or rusty edges on their back feathers and have started to show some sun bleaching. The bird on the right, with a casual look, might be mistaken for a female but it is just an immature that has the edges worm completely off and the sun has turned its back pretty rusty. The key here is to look at the elongated swelling at the top of the tarsus or below the heel of the leg structure. This mass of vessels allow for quick leg growth in young birds. This swelling is visible well into the winter and is something to look for later in the season to help separate adults and immatures.