But, the bird is unable to exercise without significant difficulty in breathing. Because the bird is markedly obese.
Obesity is a major cause of disease in cockatiels.
Although there are certainly many other causes for exercise intolerance, this column describes how birds become obese and the effect that this excessive fat has on their ability to breath. The most common cause of obesity is malnutrition, specifically an improper balance of nutrients. Most significant is excessive fat in the diet. Birds like high fat seeds and will often select them over any other seeds in the mix. Heredity appears to be another significant cause of obesity.