Using the same words over and over can make the plot flat, but Hiaasen's writing style is dynamic and active. Plus, we get way more information about characters with phrases like "Roy glanced around anxiously" (2.97), "Curly thought sourly" (11.57), and "Dana grinned malevolently" (15.47).
Adverbs: they're your friends.
But at the same time, Hiaasen doesn't try to impress you with language that sounds as if it came out of a Word-of-the-Day calendar. He gives direct characterization, and he's super-straightforward with the plot and dialogue.
Take this excerpt for example:
Overhead, a small dusky-colored bird was flying in marvelous daring corkscrews. Roy and Beatrice watched in delight as it banked lower and lower, finishing with a radical dive toward the burrow at the center of the circle. (20.158)
Descriptive? Yes. Complicated? Nope. Hiaasen paints a picture with words that are easy to understand—no need to break out a dictionary in the middle of a paragraph.