Iodine Deficiency
If pet birds are not given a proper diet, they can suffer from nutritional disorders. One such nutritional disorder is iodine deficiency, which is common in budgerigars.
Iodine deficiency affects a bird’s thyroid gland — enlarging it from its usual size of three millimeters, to about about one centimeter, or more. (The swelling of thyroid gland, due to iodine deficiency, is called Goiter.) For birds, the thyroid gland is located in the neck and is one of the glands that maintain proper function for various bodily organs.
Symptoms and Types
Birds deficient in iodine will have a lump on its neck; this is due to the enlarged thyroid gland.
The animal will also have difficulty breathing, usually recognised as loud and harsh breaths, wheezing, and clicking. 
Some birds will have difficulty eating or regurgitate food, while others will less tolerant to stress and express behavioural problem.
Treatment
As always, follow your veterinarian’s advice to reverse the iodine deficiency. Morning Birds Liquid Iodine is often used to combat and help prevent this condition.
Prevention
Including iodine in your bird’s diet will help prevent iodine deficiency.
