Yep, I completed the Adventure with 3 birds as well.
For the 7th stage, I found it best on the first room to throw Chuck at about 70% strength with an arc, activating him to smash the pig on the balloons through to the right structure, collapsing it, and often triggering the rock thrower to take out the left structure.
For the second room, I threw Blues under the lava to destroy the right structure and the pig above/to the left, again activating the rock thrower and usually leaving pigs I could clear out with another throw (saving Chuck and the ducks).
Chuck in Room 3 usually strikes it.
I found the Ducks great on Room 4; could usually clear it with 1 or 2 throws after that, then hit Room 5 with whatever’s left.
I agree with @dezsike though; deffo took a few attempts to get done.