What is a common cause for fret marks on feathers?

Fret marks on feathers are often caused by a lack of proper nutrition. When a bird does not receive a balanced and adequate diet, it can lead to deficiencies that manifest in various physical ways, including the appearance of fret marks. These marks are typically indicators of poor feather quality and health. A diet lacking in essential nutrients such as protein, vitamins, and minerals can weaken the feathers and their growth, making them more susceptible to damage and abnormal wear.

While stressful environments and inconsistent handling may impact a bird's overall well-being, they are not the primary causes of fret marks. Stress might contribute to behavioral issues or other health problems, and inconsistent handling could lead to behavioral changes, but neither of these factors fundamentally impacts feather growth and nutrition in the way that an improper diet does.