Which of these birds does not show distinctive immature plumage in their first year?

The American Kestrel does not exhibit distinctive immature plumage during its first year, which distinguishes it from the other birds listed in the question. While many raptor species, such as the Goshawk, Red-tailed Hawk, and Merlin, have notable differences in their plumage as juveniles, the American Kestrel maintains a more consistent appearance throughout its first year.

In juvenile Kestrels, the differences in coloration and markings are subtle and do not feature the pronounced variations seen in the other species. This lack of distinctive immature plumage signifies a more uniform development in appearance, leading to the conclusion that, among the options provided, the American Kestrel stands out for not undergoing significant plumage change as a juvenile. Understanding these plumage characteristics is vital for identification purposes and for comprehending the developmental stages of these birds.