This is the only hummingbird occuring in the states near the east coast of the US, where it is quite common. Ruby-throated Hummingbirds are bright emerald or golden-green on the back and crown, with gray-white underparts. Males have a brilliant iridescent red throat and black chin, but the throat may appear entirely black in poor light. Juvenile males resemble adult females, though usually with heavier throat markings.
Top: A female. Gilsland Farm Audubon Center, Falmouth, Maine, 3 August 2015
Left: A female. Falmouth, Maine, 2 August 2015