Seeds are very high in fat and low in nutrients, it would be like us living on a diet of chocolate, potato chips and soda pop. Because they don't have a diaphragm and a hiccup is a muscle spasm of the diaphram. Due to the lack of disphragm birds breath by expanding their chest. So never hold a bird to tightly around the chest or you may mistakenly suffocate the little guy. Birds also have very efficient lungs and because of this are very sensitive to toxins.
Caged birds are closely related to their wild ancestors.
In the wild a sick bird is a dead bird therefore they don't show signs of illness until the disease is well established. Signs that your bird may be sick include, fluffed up feathers, decreased activity, a change in vocalization, spending a lot of time on the bottom of the cage, incooridination, swollen eyes, sneezing or a change in droppings or apatite. If any of these occur you should contact your veterinarian right away. The best way to transport your bird to the hospital is in his own cage. Please don't clean it before you come, empty the water but leave the food and be sure to bring any medication or vitamins the bird is taking.