This is a study on how an antioxidant rich diet affects the production of stress hormones in migrating birds. Now, their stress is created by the long flying so it's physical stress BUT both emotional and physical stress elevate the production of stress hormones so this study is easily applied to our pet birds that live under chronic stress from the unnatural conditions we provide in a human home. AND the best info we get from this is that fruits (yes, fruits, which some people believe are too high in sugar for them!) are what reduces the stress hormones!
https://www.sciencedaily.com/releases/2 ... 120209.htm