Hawks in immature plumage appear to be:

Immature hawks are indeed smaller in stature compared to their adult counterparts. This size difference is attributed to the fact that young birds, still in the process of developing and growing, have not yet reached their full physical size. As they mature and go through their plumage transition, they develop not only size but also changes in feathering and coloration that signal their readiness for adulthood.

As they age, hawks will continue to grow until they reach their adult size, which can often be significantly larger than their immature form. Understanding this developmental stage is crucial for those in falconry, as recognizing the differences in size and appearance can influence training and management practices.

The other options imply an incorrect understanding of hawk growth patterns, as they do not accurately reflect the size progression from immature to adult stages.