What feature inspired the common English name element "redstart" for both species?
Answer
The bright reddish-orange coloration of their tails
The common English name element is derived from the bright reddish-orange coloration found on the tail feathers of both distinct species.

Related Questions
What primary factor separates the American Redstart from the Common Redstart despite sharing a common English name element?Which colors primarily distinguish the striking male American Redstart?What is characteristic of the Common Redstart male's coloration?What distinguishing color do female American Redstarts display where males show orange or red?Where does the Common Redstart primarily spend its non-breeding season?What is the noted foraging technique of the American Redstart involving its plumage?What is the strong nesting preference for the Common Redstart?What feature inspired the common English name element "redstart" for both species?How many eggs does the American Redstart typically lay?Which measurement primarily characterizes the size of the American Redstart?