So, you're having trouble figuring out how to get to this pesky rat with wings.
Well, don't feel bad. You aren't alone. I spent a painful amount of time hopelessly trying to get to this pest. Let me start by telling you NOT to waste your time climbing to the top of various high places and trying to jump onto the platform, regardless of how much fall damage you would take. The game has a system in place to stop you from doing so: Alexis.
She will automatically teleport you to one of her portals if you land on the platform. There's no way to cheese it; or anything like that. The intended solution is the ONLY solution.
So, what is this intended solution? Well, let me get that ball rolling. Disco ball, to be exact.

Before you can even begin to try to reach the flying freak, you're gonna need to do some collecting. See, there's this charming old man by the name name of St. E. Knirt, who owns a quaint little shop in the town square.
He may not look like it; but back in the day, he could really throw it back. He's gonna ask you to collect several disco balls for him. I won't tell you exactly why; but trust me, it'll all make no sense in due time. Once you've collected the disco balls, you'll be able to alter the map in a way that will give you access to a new area.
Where exactly is this new area? It's pretty wild...

It's on the path up to the zoo. Specifically via the diggable dirt on the wall. There's an axle at the top of this dirt that (once you've "used" the disco balls) will open up a gate to a new cave entrance. You can then hop down, reposition the platform, climb up to the zoo path, jump up into the cave, then finally dig your way back down the wall and hop onto the newly rotated platform, where the bat of your dreams will be waiting for you.

Now that you've boarded Wingrat airlines, it's time to go over what's included with your flight. You get no nachos, no soda, no movie, and no seat. What you do get is dropped onto a precarious treelimb and left for dead; but don't worry! You're reward is just inside that knothole!

In this knothole you'll be given a simple puzzle, a red screw, a setup to get another screw in the main body of the tree, and the satisfaction of knowing you'll never have to do any of this again... unless you're doing another playthrough...

I hope this guide has been helpful; and I implore you to let me know if I missed anything here, or if you're having trouble with something else.

Thank you; and buh-bye!
-Sil