Spring Beak has two variants: Spring Beak and Axe Beak.
All of Spring Beak's spells are multi-target. Silence, will stop a character from casting magic and reverse their controls for a short time, and Balloon is similar to the "Stop" effect in Final Fantasy. Other than that, be on the lookout for Air Blast or worse, Thunderbolt. Fortunately, all it takes to destroy Spring is three good castings of Popoi's level 2 Earth Slide spell.
Axe Beak is just like Spring Beak, only this guy is fire-based. Be prepared for some burnage in this battle. Popoi's elemental of choice here would be Undine, so he needs to chill out Axe by laying the smack down on him with level 7 Freeze spells. Watch his hair movements - it determines what spells he will cast. Back and forth movements mean he casting either Fire Bouquet or Fireball, or if the hair stands on its end, you're about to eat a level 7 Lava Wave. As usual, Purim should be casting level 7 Cure Waters if anyone is injured.