How can you distinguish a passage American kestrel from a haggard American kestrel?

The correct answer highlights a key characteristic that distinguishes a passage American kestrel from a haggard American kestrel: the presence of immature wing feathers in the passage bird.

Passage kestrels are essentially juvenile birds that are migrating and may not have completed their first molt. As a result, they often exhibit immature feathers, which can be less developed and different in appearance compared to the fully formed adult feathers found on haggard kestrels. Adult or haggard kestrels have undergone a complete molt, resulting in a more uniform and mature plumage that is typically brighter and more vibrant.

In contrast, fluffiness of feathers, differences in color and condition of plumage, and size differences do not provide reliable indicators for distinguishing between these two types. Feather fluffiness can vary due to several factors, and color differences alone might not be significant enough to differentiate between juvenile and adult plumage in some cases. Additionally, size differences are minimal between passage and haggard kestrels, making size an unreliable factor for identification. Thus, focusing on the immature wing feathers provides a clear and dependable method for identification.