What is a key attribute of a 'passage bird'?

A key attribute of a passage bird is that it is a young bird that has recently left its nest. This term specifically refers to birds that are in the juvenile stage of their life cycle and are often migrating for the first time after fledging. These birds are typically between the ages of 4 to 10 months when they are considered passage birds. They are characterized by their independence from their parents and their readiness to adapt to new environments, which makes them suitable for falconry, especially for training and hunting.

The significance of this attribute is that passage birds are often more robust and adaptable compared to older birds, which can lead to better performance in falconry practices. In the wild, they are still learning and growing, and their youthfulness adds an extra layer of training potential for falconers.

The other options refer to different life stages or usages of birds that do not align with the specific definition of a passage bird. Therefore, focusing on the accurate definition ensures clarity in understanding the various classifications of birds relevant to falconry.