What causes fret marks on the feathers of a new bird?

Fret marks on the feathers of a new bird are typically caused by a combination of arrested feather development and stress. Arrested feather development occurs when the feathers do not grow properly, often due to insufficient nutrients or environmental factors, which can lead to atypical feather structure. When this happens, feathers can become prone to having these characteristic fret marks, which are often seen as irregular or damaged lines along the feather.

Additionally, stress plays a significant role in the appearance of fret marks. Birds can experience stress from various sources, such as changes in environment, handling, or competition with other birds. This stress can disrupt normal feather growth and lead to these visible marks.

Together, these factors explain why fret marks appear, as both arrested development and stress directly influence the health and condition of the feathers as they mature. Understanding these conditions is essential for ensuring proper care and management of raptors in falconry.