Squirrel

Squirrels are a small mammalian species native to Earth on several continents. Squirrels are herbivorous, eating a basic diet of nuts, small plants and seeds. They also live in trees in order to hide from predators and to raise young.

On Other Planets
Similar animals, also referred to as "squirrels", have been noted to live on several planets, including Reach until its destruction by the Covenant.

The young Spartan-IIs survived several days on squirrels during one of their war game sessions with Tango Company, where they had to capture a flag.

Janissary James, musing about food in which milk that came from an unspecified source is used, suggested that the milk could come from squirrels.

Trivia
The Halo: Reach Squirrel AI; jokingly referred to as the "Space Squirrel", was deleted from the game after it, like the Porcupine, failed to succeed the "Zero-bug release" tests.