These microorganisms are the result of disease, NOT the cause of it. When a bird experiences stress, either physically or emotionally, its metabolic response is to activate the sympathetic nervous system. Some of the physiological changes that take place are increased sugar and fats into the bloodstream, the production of more adrenaline, cortisol, and glucagon into the blood, a decrease in digestive function, increased blood pressure, heartbeat, breathing rate, muscle tension and, thus, the creation of more energy. Consequently, the bird may react to stress by channeling the body's response to physical distruction, such as feather picking itself or a cage mate, which can be difficult to eradicate once it becomes a normal psychological response. Stress may also manifest inward to one of the organ systems, such as the nervous system, circulatory, or digestive system.
Stress increases the metabolism of proteins, fats, and carbohydrates.
There is an increased excretion of amino acids, potassium, and phosphorus and a decreased storage of calcium. Vitamin C and other important nutrients are also excreted at a faster rate. During stress, nutrients are depleted from the body rapidly and the immune system becomes depressed. In essence, when a bird is under stress, its whole body is affected. Chronic stress can harm the nervous system, thereby causing digestive and intestinal upsets.