If the scales of a bird's shank appear crusty and swollen, what is likely the issue?

The presence of crusty and swollen scales on a bird's shank is indicative of a condition known as scaly leg mites. These microscopic parasites burrow under the scales of the bird's legs and feet, causing irritation and resulting in the characteristic swelling and crustiness. This condition is commonly seen in poultry and can lead to significant discomfort and potential health issues for the bird if left untreated.

In contrast, while a fungal infection could cause skin issues, it would typically present differently than those seen with scaly leg mites, often involving lesions or discoloration rather than just crusty scales. Broken bones would usually be associated with visible signs of pain or mobility issues but would not specifically cause the crusty scale appearance. Heat stress can lead to a variety of physiological responses, but it would not result in the specific symptom of swollen, crusty scales on the shank. Therefore, the description of the shank condition strongly points to scaly leg mites as the primary issue.