Henry and the Crazed Chicken Pirates by Carolyn Crimi, illustrated by

From chapters.ca:
Barnacle Black Ear and his band of Buccaneer Bunnies are busy - shooting one another out of cannons; swinging from the masts of their ship - too busy to listen when Henry finds a threatening message in a bottle. While Henry works frantically on his book, Henry's Plan for Impending Danger from the Unknown Enemy who Wrote the Scary Note, his mates bowl with coconuts or dig for treasure, and his father, Black Ear, bellows that Henry is wasting his time. But when Crazed Chicken Pirates attack the unsuspecting Bunnies, will Henry and his book save the day?