From Halopedia, the Halo wiki
Ghost squirrels, also known simply as Dwarkan squirrels are small, quick, toothless "squirrel-like" creatures which lived on the human colony planet of Dwarka in the forests surrounding the childhood home of Soren-066. Aside from their appearance, their behavior is also known to have been akin to Earth squirrels; for example, when Soren hit one with a rock it chittered angrily at him before scuttling away. On one occasion Soren was able to kill one and eat it, however he found its meat spongy and bitter. After that, he stopped trying to catch them. 
The planet Dwarka was glassed by the Covenant shortly after the beginning of the Human-Covenant War, and it is unknown whether the Dwarkan squirrel species survived the destruction of its homeworld, or whether it had been transplanted onto other planets.
List of appearances