n large animal swarm 

Perception +9; low-light vision

Skills Acrobatics +10, Thievery +10

Str +0 Dex +3 Con +0 Int -4 Wis +4 Cha +0

AC  19; Fort +7, Ref +12, Will +9

HP 30; Immunities precision, swarm mind; Weaknesses area

Speed 10 feet, fly 40 feet

Enraged Cunning There are few things as dangerously persistent in the natural world as an angry unkindness of ravens. A raven swarm can hound its prey through most barriers. Simple latches, unsecured chimney flues, loosely shuttered windows, and similar obstacles rarely keep an unkindness away. A raven swarm attempts a Thievery check to bypass many of these simple obstructions, typically against DC 20.

Swarming Beaks [>] The ravens' angry pecking deals 1d8 piercing damage to each enemy in the swarm's space (DC 20 basic Reflex save). A creature that critically fails its save is blinded for 1d4 rounds as the ravens focus their attacks on the target's vulnerable face.

Bestiary 2, page 221.