The Ruby-throated hummingbird is the only hummingbird to breed
East of the Mississippi River. However, the Rufous hummingbird is a
migrant (meaning that it occasionally) ventures out of its
territory. So the Rufous has been spotted in Pennsylvania
rarely.
The Ruby-throated hummingbird is easy to identify. The
iridescent feathers on the neck(gorget) of the male Ruby-throated
are ruby colored in sunlight.