In the natural environment, birds may frequently experience periods of starvation or dehydration, as a result of restrictions in food or water availability, temperature extremes, ecological competition and some migratory, sexual and nesting behaviour. In this paper the involvement of pituitary (growth hormone and luteinizing hormone), thyroid (thyroxine and triiodothyronine) and adrenal (corticosterone) hormones in the birds homeostatic response to these stresses has been investigated in ducks (Anas platyrhynchos) deprived of food or water for up to 36 h and in ducks additionally stressed by prior adaptation to hyper-osmotic drinking water and/or acutely orally loaded with crude North Sea oil. Variations in the peripheral plasma concentration of these hormones during food or water deprivation have also been correlated with stress induced alterations in body and organ weights and with accompanying changes in circulating sodium, potassium and glucose levels; their physiological roles during stress are discussed.