Blindsense( Complete Adventurer, p. 114)
You can sense creatures that you cannot see.
Listen 4 ranks, Wild shape class feature,
You can expend one daily use of wild shape to gain blindsense for 1 minute per Hit Die, enabling you to pinpoint the location of a creature within 30 feet if you have line of effect to that creature (see page 306 of the Monster Manual). You retain this benefit regardless of what form you are in.