Bird thyroid disease is most often caused by a deficiency in iodine in the bird’s diet. Birds have two separate pairs of thyroid glands (unlike most mammals, who have a single pair). The glands are located in the neck; normal thyroid glands cannot be felt from the outside of the bird because of their location within the bird’s thoracic cavity. The thyroid controls the rate of metabolism in the bird, through the release of a chemical known as thyroxine. If the thyroid glands become enlarged, a condition known as goiter results. Birds on an all-seed diet, or a diet that is made up mostly of seed, are most at risk for an iodine deficiency. At the other end of the spectrum, birds that take in an excessive amount of iodine can also be at risk for developing goiter. When the thyroid glands become enlarged, they can put pressure on the bird’s syrinx, or “voice box,” which can cause a loss of voice or very raspy sounding voice. Birds with enlarged thyroid glands, or goiter, may also frequently regurgitate, due to pressure in the throat while trying to swallow. A squeaking sound during breathing can also be an indicator of pressure being placed n a bird’s lungs or air sacs, due to bird thyroid disease. Birds with thyroid disease are also at risk for other illnesses, because their immune systems are suppressed by the thyroid malfunction. With a decrease in their metabolic rate, bird thyroid disease often causes birds to become lethargic and overweight. Skin and feather problems can also be a result of bird thyroid disease, as can reproductive problems. Hens suffering from thyroid disease may not produce as many eggs. Of the eggs laid by a hen with thyroid disease, a lower rate of successful hatches is common. Bird thyroid disease is often diagnosed through blood tests or sometimes through radiographs such as x-rays or scans. Once diagnosed, treatment for bird thyroid disease usually includes an iodine supplement. This is most often given in the form of drops added to the bird’s water supply. In the case of a bird with a severe iodine deficiency, it may be necessary to place the bird in a special, oxygen-rich environment and administer injections of sodium iodide. In the long term, an increase in iodine in dietary forms and decreasing foods such as cabbage, broccoli or turnips, which can prevent proper thyroid function, can be better for your bird than simply administering iodine supplements.