Warning: This is 3.0 Edition material. It is possible that there is more recent 3.5 Edition version.
Inaccurate?

Deep Denizen

( Savage Species, p. 32)

[General]

You are adapted to a subterranean environment.

Prerequisite

Underground as sole terrain type,

Benefit

Living underground has made you more reliant on nonvisual senses than surface dwellers. You gain a +2 competence bonus on Listen checks and a +4 competence bonus when tracking by scent.