haven't heard of that on birds... i did hear of birds having something in their brain which is electromagnetically tuned to the earth though. other animals have it as well im sure. it would be why they migrate, or always seem to know when to take high ground before a tsunami...
i saw a thing about the organ on sharks, it's not a "third eye" but instead of a sense of smell, it has in a similar location, a sense organ that is adapted to behighly sensitive to vibration (EM waves are vibrations). so in this sense, it can visualize in it's mind where things are in the water. like echolocation but through liquid.
conceptually, it's like a third eye, but really, it's like if your ears and nose adapted into a singular organ (because neither have practical use underwater the way they are) and are therefore amplified in power. i can see the practicality of this, namely because of the increased speed which vibration travels through denser mediums (solids>liquids>gases)