What behavioral display do both sexes of *T. verticalis* use when attacking much larger birds to defend territories?

Bill-snapping and flashing their normally concealed crimson crown feathers

The aggressive disposition that grants the Western Kingbird its moniker is intensely demonstrated when defending breeding territories against perceived threats, including significantly larger avian predators such as Red-tailed Hawks and American Kestrels. This defense mechanism involves active physical threats combined with visual displays. Specifically, the birds engage in bill-snapping motions directed at the threat, coupled with the dramatic action of flashing their normally concealed crimson crown feathers. This flash of color serves as a potent visual signal of aggression and fitness. This evolved aggression is critical because nest predators, including snakes, owls, and ravens, account for a substantial portion of nest losses, making aggressive defense a high-fitness survival strategy for protecting their reproductive investment.