This video from the USA says about itself:
Juvenile and Adult Male Rivoli’s Hummingbirds Swap Time In West Texas — Sept. 13, 2017
The heavy traffic on the West Texas hummingbird cam provides a great opportunity to compare plumage differences within the same species. Here, a pair of eye-catching male Rivoli’s Hummingbirds swap time at the feeder. An immature male, with his scaled plumage, light green back, and iridescent green splotched throat stops in first. Soon he will exhibit the blackish, dark green body, brilliant teal gorget, and purple crown like that of the adult male that hovers in after him.