What is the term for the act of a bird releasing waste?

The term that correctly refers to the act of a bird releasing waste is "Mute." In falconry and bird handling contexts, "mute" describes the specific droppings produced by birds, often serving as an important indicator of their health and diet. Falcons and other birds of prey produce mutes that are typically composed of a combination of urates and feces, which is a vital aspect for falconers to monitor.

The other terms listed refer to broader or less specific concepts regarding waste elimination. For example, “excretion” is a general biological term applicable to all animals and is not unique to birds, while “evacuation” is often used in more casual contexts and doesn’t specifically pertain to avian waste. “Drop” could imply dropping something in a more colloquial sense but does not accurately capture the specific meaning regarding bird droppings. Thus, "mute" is the precise term that falconers and ornithologists use to discuss bird waste.