What distinguishing behavior does the Kirtland's Warbler exhibit while perched?

Answer

Constantly bobbing its tail up and down

Behaviorally, the Kirtland's Warbler is easily spotted by its habit of constantly bobbing its tail up and down while perched, a motion uncommon among many northern warblers.

What distinguishing behavior does the Kirtland's Warbler exhibit while perched?

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I Tracked Down the RAREST Warbler in the United States! - YouTube

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