Which of the following is an indication of unmanaged stress in birds?

Fret marks are indeed a clear indication of unmanaged stress in birds. These marks, which can appear on the skin or feathers, arise from excessive preening or self-mutilation often associated with stress and anxiety. When birds experience high levels of stress, they might engage in behaviors like over-preening as a coping mechanism, leading to noticeable damage in their plumage or skin.

In contrast, healthy plumage typically signifies a well-adjusted and stress-free bird. Frequent vocalization can be a natural behavior and may not necessarily indicate stress, as many species vocalize for various reasons, including communication or expressing excitement. Similarly, an increased appetite is often a sign of good health or normal behavior rather than stress; decreased appetite is more commonly associated with stress in birds. Therefore, the appearance of fret marks is a distinct signal pointing towards unmanaged stress in avian species.