The term "rouse" refers to:

The term "rouse" specifically refers to the action of shaking feathers to settle them back in place. This behavior is commonly observed in birds as a way to restore order to their plumage, which can become disheveled during activities like preening, flying, or resting. When a bird rouses, it helps ensure that its feathers are aligned properly, which is essential for maintaining insulation, waterproofing, and aerodynamic efficiency necessary for flying.

In contrast, the other choices describe different behaviors or states not directly related to the act of rousing. Active hunting refers to the engagement in pursuit of prey but does not involve feather care. Fluffing feathers while being alerted involves a different physiological response, often associated with comfort or regulating body temperature rather than settling feathers. A display of aggression can be shown through various postures or behaviors, but it is not specifically linked to the act of rousing. Thus, the focus on feather maintenance distinctly defines why "rouse" is best described by the action of shaking feathers to settle them back in place.