Foot mutilation is a problem that has plagued many birds. It is a form of self mutilation that may have many different causes. It may start due to a medical problem and be perpetuated due to stress-related behavior issues. Please see my discussion on mutilation/feather-picking for my opinion of the various stress-related causes of mutilation.
Here is a link to that discussion: http://www.mytoos.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=10&t=000604#000005
There have been a number of medical causes that have been identified as inciting factors involved in foot mutilation. There have also been several theories advanced (pure speculation, in some cases) that unfortunately have been perpetuated in the literature to the point where they are now accepted as having been well documented – when in reality, they remain pure speculation with no proof that they are involved at all.
Some of the well documented causes include:
1. Inflammation secondary to injury
2. Contact with substances that cause inflammation in the skin, such as disinfectants, soaps, cosmetics, and residue from cigarette smoke on owner's fingers (among others)
3. Circulation disorders in the foot or toes caused by infection or trauma or systemic disease (especially liver disease)
4. Infections with bacteria or fungus that are usually secondary to numbers 1 or 2 above.
5. Infections with herpes virus is a cause that is somewhat better documented, but still not proven. Years ago, there were a number of reports of foot necrosis in wild-caught Amazon parrots. Someone actually observed herpes virus particles by electron microscopy in a sample scraped from the foot on one affected Amazon. Some others responded to a cream used to treat herpes virus in people. It may be that there was herpes virus infection in some of these Amazons, but they were probably infected during exposure to other species of birds (especially poultry) while in the holding and shipping facilities associated with their import to this country. It is not a disease that is likely to be found in domestically raised parrots, unless they have been exposed to older wild-caught Amazons.
One of the theories that remains completely unproven is hypothyroidism. This is a disease that involves the lack of production of thyroid hormone by the thyroid gland in the neck. In people and other mammals, it causes a variety of symptoms (NOT including self mutilation) that are related to a metabolic rate that is slowed by the low levels of thyroid hormones. These include obesity, lethargy (lack of energy) and thickening of the skin and poor hair coats. In mammals, it is diagnosed with a test that involves stimulating the thyroid gland with a hormone that the brain normally produces to stimulate the production of thyroid hormone. When this hormone is given, the thyroid should respond by producing more thyroid hormone and this increase can be measured. If it does not, then a diagnosis of hypothyroidism is made and the thyroid hormone is given daily as replacement therapy. The thyroid gland may fail to produce thyroid hormone due to infection, cancer, or a failure of the pituitary to provide the stimulating hormone. The replacement hormone therapy usually must be given for the rest of the animal's (or human's) life. It causes an increase in the metabolic rate and can be very dangerous if overdosed or given based on a false or incorrect diagnosis of hypothyroidism.
For many years, lots of people have speculated that skin and feather problems in birds may be caused by hypothyroidism. Unfortunately, the same tests used to evaluate their thyroid do not accurately give information about the health and function of the gland.
There have been a number of well designed scientific studies that have nevertheless failed to produce an accurate and reliable protocol for diagnosing hypothyroidism in birds. The stimulation test is not reliable and simply measuring the levels of the various forms of thyroid hormone do NOT accurately reveal the true health or function of the gland in birds. For that matter, measuring these hormones in people and other animals is also not considered to be a reliable way to diagnose hypothyroidism.
There is only one single report in the veterinary literature that claims to have accurately diagnosed hypothyroidism in a macaw. This report is considered by many to be flawed, as it has not been possible for other researchers to duplicate the results. It is true that in this report, the macaw seemed to improve the feather quality when given replacement therapy, but it is possible (and I believe probable) that the increased metabolic rate caused by the hormone replacement was really addressing an underlying slowed metabolic rate caused by some other factor – possibly related to diet – possibly related to reproductive hormonal pressure and changes.
Many birds have been given replacement thyroid hormone without a diagnosis and have suffered heart and other conditions caused by this treatment. I have seen several birds who have actually died from heart failure when given thyroid hormone, so in light of the inability to accurately diagnose hypothyroidism in birds and the fact that the treatment can be dangerous, great caution should be exercised in dealing with this possibility. This caution should come in the form of very meticulously ruling out ALL other possibilities before focusing on this as a cause.
Finally, even if a medical problem is responsible for a cockatoo or other imprinted parrot to begin to mutilate the feet, it is extremely common for this mutilation to continue and get worse due to the behavior issues involved. This includes attention-getting behavior. If you focus on this activity and act concerned about it, the bird will almost certainly learn that this is a behavior that will result in your focused attention. There is no better reward for a dependent, imprinted parrot for a behavior than the focused attention of the human (s)he is imprinted on. In the wild, they are in contact with their bonded flock members 24 hours/day. In out human/bird flocks, this is rarely the case. Their natural behavior of attention-getting is probably responsible for the bulk of minor medical problems to escalate into very major, even life-threatening ones. I have known a number of cockatoos to chew toes OFF the OTHER foot after the owner has focused too much on a minor injury or infection on a foot.
The bottom line is this: A very thorough medical workup, followed by a very complete behavior analysis is necessary to successfully resolve these cases. When frustrated by a behavior case that no answer is easily being identified, it is very tempting to start looking into “left field” for those reported possibilities. Please be very careful about chasing these highly unlikely diagnosis and look carefully for exaggerated natural behaviors that are often involved in this difficult syndrome.