Ruth Stiles Gannett

When Elmer Elevator tells a stray cat about his dream of being able to fly, he learns of a captive dragon on Wild Island. The dragon has been forced by the jungle residents to serve as their shuttle across a wide river — and anyone who rescues the dragon from its cruel captors might be entitled to a free ride.
Elmer needs no further encouragement to stow away aboard a ship to the island, where he matches wits with hungry tigers, an irate...

On their way home, Elmer and a flying dragon land on an unusual island and help some canaries uncover a buried treasure. Sequel to "My Father's Dragon."