Answer: Horses

When it comes to getting by on little sleep, even the most caffeinated human worker has nothing on horses. Horses have very little in the way of sleep demands with the average horse spending four to fifteen hours a day on their feet in standing rest and a few minutes to several hours lying down, but only requiring around two and a half hours of actual sleep (occurring in many short intervals of about fifteen minutes each).

Not only do horses get by on very little sleep, but they can sleep both standing up and lying down. Although they may lay down more than once per day, horses only need to lay down (a requirement to reach REM sleep) for an hour or two every few days to meet their minimum REM sleep requirements. Horses stressed by the presence of predators or other stimulus in their environment may even go days without entering into REM sleep, but will eventually collapse, even if for a few minutes, to enter a deep sleep state and catch up.

Horses are hardly alone in their truncated sleep patterns, however, especially among grazing animals. Giraffes also sleep very little and spend most of their time on their feet—grazing animals need to maintain near constant alertness to ward off predators and escape quickly from danger.