In falconry, a "passager" is most likely to be...

A "passager" refers specifically to a young bird that has recently been captured in the wild, typically one that is still in its first year of life and not fully fledged. This term is often used in the context of falconry to describe an immatures raptor that has not yet gone through a full migratory cycle. The significance of capturing a young bird lies in the opportunity to train it from a relatively early stage of development, which can result in a strong bond between the falconer and the bird as well as a more responsive and effective hunting partner.

Choosing this designation helps establish clear communication within the falconry community, as it specifically denotes the age and capture status of the bird, distinguishing it from other categories like mature raptors or those captured at different times of the year. Being familiar with such terminology is essential for understanding the nuances of falconry practices and bird behavior.