Toucan island is an unlockable island in Harvest Moon: Tree of Tranquility and Animal Parade. Some of the residents of the island are Sue and Samson (who run the Pineapple Inn), the parents of Selena (in Animal Parade Selena is also living on the island). Toucan Island is a tropical island, with special fruits not available on the mainland, such as Pineapples and Bananas (required for Collin's rainbow in Tree of Tranquility). It is also a good fishing spot.
Harvest Moon: Tree of Tranquility
In Harvest Moon: Tree of Tranquility it is unlocked after you've finished Daren's Rainbow. Talk to Pascal at the dock, who will ask you "do you want to go to Toucan Island?". Say yes, if you want to go to Toucan Island, and you will travel there via ferry. The first time you visit Toucan Island, Sue will ask you to deliver a message from her to Selena. If you deliver this message and return to Sue on Toucan Island she will reward you with a Manta Ray.
Harvest Moon: Animal Parade
In Harvest Moon: Animal Parade it is unlocked after you ring the Blue Bell. The boat ride to the island costs 400 G. You can buy boat tickets form Ozzie's shop when he's open, and then hand them over to Pascal on the boat dock in Harmonica Town. The return trip is included, but it you have unlocked the animal taxi service, you can leave the island by using the circus animals.