What is a common sign of a relaxed bird?

A common sign of a relaxed bird is indeed puffing out feathers. When a bird feels comfortable and at ease, it may fluff up its feathers as a way of regulating body temperature and demonstrating a relaxed state. This behavior allows air to circulate between the feathers, providing insulation or a cooling effect, depending on the environment. It is a natural way for birds to showcase their comfort in their surroundings.

The other options do not accurately reflect signs of relaxation. For instance, feeding until full may occur in a relaxed state but is not a definitive sign of relaxation itself. Stretching wings defensively typically indicates a state of alertness or readiness to protect oneself rather than relaxation. Temporary release into the wild involves a significant amount of stress and adaptation for the bird, which is contrary to the concept of relaxation. Therefore, puffing out feathers is the most accurate indicator of a relaxed bird.