Scaly Leg is most commonly caused by Knemidokoptes - also spelled Cnemidocoptes, which are eight-legged microscopic mites that are related to spiders, ticks and scorpions - but obviously much smaller in size. They burrow in the feet and legs, but may also affect the vent and face.
Different species of mites affect different species of birds. Knemidokoptes are most frequently found in budgies; however, they have also been reported in other species of birds. In canaries and finches, the same mite causes a condition commonly called 'Tassle Foot'. It is also likely that some birds are genetically more susceptible to these mites than others.
These mites are very contagious; therefore, if one bird has it, all birds that it came in contact with need to be treated.
Secondary bacterial infection and arthritis may occur.
It is thought that in many instances, these mites are acquired in the nest, with the infection remaining latent for a long period of time. Early signs of this disease may be seen after six to twelve months.
Scaly leg mites bore under the scales on the legs of the bird.
Feet or legs have a crusty, scaly appearance, which may also sometimes appear around the vent and wing tips (as well as the face and beak).
Legs / feet may look swollen.
The claws may become overgrown and cracked.
The scales may become infected.
Heavy scaling and overgrown claws can result in lameness / reduced mobility, inability to perch and increased discomfort in the bird.
In Canaries, their legs develop thickened areas that look more like corns.
NOTE: Older canaries can naturally develop scaly legs that don't have anything to do with mites, but are instead an indication of a build-up of calcium salt between the scales of a canary's feet and legs. Younger canaries usually don't have these scales, although some canaries are susceptible to having the calcium salt metabolism problem their whole life. However, as a general rule, scaly legs in YOUNG canaries are most often (but not always) associated with scaly leg mites.
In Pigeons, a type of knemidokoptes causes severe itching and this is often referred to as "depluming scabies". These mites tunnel into feather follicles and feather shafts causing severe itching and feather loss.
The lesions typically develop very slowly, so that an infected bird may appear normal for a long period of time.
Advanced infestations spread to the unfeathered parts of the body.
If left untreated, the bird will succumb to the disease.
The vet will take a scraping of the affected areas. The mites are present and are visible under a microscope.
Advanced cases have characteristic crusty / scaly lesions.
Other possible causes:
Any swellings can be caused by strangulated fibers or insect bites.
Nutritional Deficiency: Birds deficient in vitamin A are particularly susceptible to this condition. Seeds are typically low in vitamin A. This vitamin promotes appetite, digestion, and also increases resistance to infection and to some parasites.
The most obvious sign of a vitamin A deficiency is a feather stain above the cere. The staining of the feathers above the nostrils reflects a discharge from the nostrils. Subtle differences may be seen as far as the color intensity of the cere and feathers is concerned - and the overall condition of the plumage. A bird deficient in this vitamin may have pale, rough-looking feathers that lack luster. The cere may look rough instead of smooth, and you may see an accumulation of a yellow dry scale on the sides of the beak.
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