You use the bells at the bird roost's to call her to pick you up and go to another roost. If you don't have the floaties to swim I believe you race the dude to the south of that area or something.
TY not as used to the dynamic of context sensitive locations for item use. Seen such in games before but only verry rarely.
Where is the bird roost in main island?
Should be just south of the broken bridge
But I only found 3 planks and was sent back to the main island. Damn. I need to replay now.
Once you do that you unlock the ability to get something that lets you get across again.