Iggy is the first member, and is the least intelligent. He is extremely unaware of what he's doing and acts crazy, although he does seem to know the difference of a bird and pig. Iggy is not a fierce adversary as he just drops wood to construct structures to block your path. His structures can be easily bypassed or destroyed, allowing you to easily defeat him.
Piggy is the next member and is the brains of the group. He is very intelligent and knows how to build and heal pigs, but knows little of how to battle, so he is an easy fight. His attack is to fire pigs at the birds to stop them, as well to build. This may seem difficult, but because of the random placement of buildings and the slow firing rate of the cannon, he is an easy boss.
Zach is the final boss of the trio and is the captain and the brawn of the group. He is of average intelligence and knows mainly how to build and to take care of birds. He is the most difficult boss of far, he fires at birds and builds structures similar to the other two bosses, and can spawn in pigs to block the player. The cannon is much faster than in the Piggy fight, and the buildings are placed better. He is a very hard boss compared to the others.