Your expertise aids you against many similar foes.
Once per day as a swift action, you can change the subtype of the humanoid or outsider you chose as your favored enemy. For example, you can change your favored enemy from humanoid (elf) to humanoid (dwarf). The bonus granted by favored enemy when used in this way is always +2, regardless of the original bonus. This change lasts for a number of rounds equal to your character level.
You can gain this feat multiple times. Each time you take the feat, you can use this ability one additional time per day.
The text on this page is Open Game Content, and is licensed for public use under the terms of the Open Game License v1.0a.
Sources:
SECTION 15