During the summer, what characteristic defines the Eastern Kingbird's breeding range geographically?

Answer

It occupies nearly every state east of the Rockies, save for the driest southwestern deserts

The summer range is widespread across the eastern temperate zone, encompassing almost all states east of the Rockies, with the exception of the driest deserts in the southwest.

During the summer, what characteristic defines the Eastern Kingbird's breeding range geographically?
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