A bird that is very comfortable with its surroundings is likely to:

A bird that is very comfortable with its surroundings is likely to rouse, which refers to the bird's behavior of stretching and fluffing its feathers, often while perched. This activity helps to invigorate the bird and can involve shaking out its feathers, which can promote warmth and readiness for flight.

When a bird feels secure and relaxed in its environment, it is more likely to engage in natural behaviors such as rousing. This indicates a level of comfort and safety, allowing it to focus on grooming and stretching rather than being on high alert for potential threats.

The other options pertain to different behaviors. For example, gorging refers to excessive feeding, which is not directly related to the bird's comfort in its surroundings. Hacking involves a process of acclimatizing a young bird to its environment, but it implies a more transitional phase rather than a comfortable state. Rangle is not a standard term in the context of bird behavior in falconry, making it less applicable. Hence, rouse is the behavior that correctly reflects a bird's interaction with a familiar and safe environment.