Scaley skin is a common problem in captive birds.  On the feet the skin may appear as a white powdery to flakey substance, or develop a thick build-up of dry yellow material.  On the body beneath the feathers you may see a spiderweb of dry skin, sometimes with patches of yellow or tan crusts.  Scaley skin can be caused by a variety of problems.  An imbalanced, particularly one that is low in vitamin A or ones that have an imbalance of other nutrients, is a common cause of dry flakey skin on the feet and under the feathers.  Ectoparasites such as mites can cause thick build-up of skin on the legs of some birds.  The actual type of mite varies depending on the bird species.  For example, a parakeet may develop a beak with a crusty honeycomb appearance due to infestation with Knemidokoptes mites.  

Parakeet with classic signs of Knemidokoptes mites.

The actual Knemidokoptes mite is found by scraping the affected beak and leg scales.

Bacterial and fungal skin infections may also cause the skin to develop a scaley appearance.  Other medical conditions such as liver disorders and hypovitaminosis A can make the skin appear unhealthy too.  If you notice a chance in your bird's skin, or your bird has skin that looks like these pictures, a trip to the veterinarian is essential to determine the real cause and begin treatment!

Dry flakey skin due to vitamin A deficiency