Feather Loss in Birds
All birds, including cockatiels, start to show symptoms of any condition only after the condition has become severe. It is extremely important to see an avian vet as soon as there is any change in either the appearance or the behavior of your cockatiel. Molting is normal and a cockatiel can spend hours preening and plucking at his feathers. Since they cannot groom their heads, they often rub themselves against the bars of their cage in order to get rid of the old feathers and allow newer ones to take their place. Repeated rubbing in a single area could cause a temporary bald patch in birds which would soon be covered by newer feathers. It generally takes about 3 days or so for the new feathers to come through so if your cockatiel has had this bald patch for over 3 days, you can eliminate molting as a cause.
Irritants, especially chemical irritants could be the root cause of the problem. Toxins from fresh pain, cleaning solutions, and detergents can have a very severe effect on the delicate systems of a bird. If you have started using a new solution when cleaning your birdcage or the coop cups, this could be the problem. Make sure that you always use mild cleaning products that are suitable for birds when cleaning a birdcage. You should also rinse the entire cage thoroughly with very warm or hot water to get rid of any surfactant reside.
Bird mites are another possible cause for bald patch in birds above his eye and so you will need to check for some of the classic signs of a bird mite infestation. If he has been preening more than usual or if he is extremely restless and keeps ruffling his feathers, it is probably due to the presence of mites. You will need to talk to your vet before you treat either your cockatiel or his environment.
Make an appointment with your vet and before you go in jot down any changes that you have noticed. Keep an eye out for changes in his dropping as well as in his eating and drinking habits. If you have not noticed any changes in his behavior or if you have specifically noticed that certain habits have remained unchanged make sure that you point it out to your vet. Do not delay treatment or else the condition may get worse and the recovery process will be unnecessarily prolonged.