n large animal swarm 

Perception +10; echolocation (precise) 20 feet, low-light vision

Skills Acrobatics +7, Athletics +4 (+7 to Climb), Stealth +7

Str +1 Dex +4 Con +1 Int -4 Wis +3 Cha -3

Echolocation A bat swarm can use its hearing as a precise sense at the listed range.

AC  15; Fort +6, Ref +9, Will +6

HP 11; Immunities precision, swarm mind; Weaknesses area damage 3, splash damage 3

Speed 5 feet, fly 30 feet

Blood Feast [>] Each enemy in the bat swarm's space takes 1d4 piercing damage (DC 16 basic Reflex save). Creatures that fail this save also take 1 persistent bleed damage.

Bestiary, page 39.