From what behavior does the perception of aggression in scissor-tailed flycatchers almost entirely stem?

Answer

Fierce protectiveness during the breeding season

The perception that these birds are aggressive arises almost entirely from their vigorous defense of nesting territories against any perceived threat, including humans, during breeding time.

From what behavior does the perception of aggression in scissor-tailed flycatchers almost entirely stem?
behaviorbirdFlycatcheraggressivity