Why is identifying Ruby-throated Hummingbirds straightforward in the East during their breeding season?

Answer

It is the only species regularly found east of the Rockies during breeding season

The Ruby-throated Hummingbird is the only species regularly found east of the Rockies during the breeding season, which makes identification straightforward in the East.

Why is identifying Ruby-throated Hummingbirds straightforward in the East during their breeding season?
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