To stay healthy, birds must keep their feathers clean from dirt and parasites, and to keep their feathers in order.
They will use their bills and feet to stroke every feather from its base to its tip. Most birds will clean (preen} several times a day.
In time this young buck nubs will become antlers. His coat (hair} is now changing to over to his winter coat, which is thicker and longer. That will help him to stay warmer in the winter months.
This is my favorite picture of a bird. I wonder what the bird was thinking as she looks into the eyes of the statue of the girl. The Downy Woodpecker, female, photo was taken one winter day with snow on the ground.