We humans must deal with stress as part of our everyday living. Likewise, birds must learn to deal with certain amounts of stress. As their caretaker, however, we must try to minimize this stress and provide our birds with the best care possible. Proper care includes balanced nutrition, fresh water, clean cages, proper vet care, and a consistent amount of attention and affection. A cage without toys and stimuli also causes stress.
Stress management works for people, and it can work for our birds.
Consider the things in your bird' environments, and try to identify and eliminate the stressors you may find. Rats or mice scurrying around your aviary will stress your birds, and we know stress can cause infertility. Make sure your bird eats a nutritious diet, and supplement the diet with appropriate vitamins and minerals, as directed by your vet. Vary the diet to ensure a broad range of nutrients. And if your bird does get sick from the stress of breeding, or from other stressors, take it to an avian vet immediately for diagnosis and treatment.