The Flying Beaver Brothers: Birds vs. Bunnies: 12/15/15
The Flying Beaver Brothers: Birds vs. Bunnies by Maxwell Eaton III is the fourth in the series. The brothers Beaver have decided to head off on a well deserved vacation on a neighboring island. Unfortunately they land on one that's in the middle of a feud between the birds and the bunnies.
As with the other books in the series there's a giant machine based on something recognizable (like a giant fan). There are guarded bases and prisons. There is also usually a mastermind behind the plan.