Most of the time with dogs or cats or kids, you know right away if they are feeling bad. They show very visible and obvious signs of distress or illness. Then there are the birds.
Birds are notorious for hiding or concealing the visible signs of illness.
Birds are genetically programmed to conceal sickness or infirmity because in the rain forest or tropical habitats of their origin, predators are ever vigilant for the weak individual. Predators target sick animals because they are easy prey, slow, and require little energy investment in the hunt. In your home, then, you and your family become the perceived predators to a sick bird. Because birds hide their signs of illness so well, you must learn to look for signs of sickness. Look at your bird prior to opening doors or going into its room and turning all the lights on in the morning.