Many people think that gerbils are either diurnal (active during the day) or nocturnal (active during night). Some even say that they are crepuscular, meaning that they are active during twilight.
But in fact their activity cycle is a bit more complex. The Mongolian gerbil isn’t only awake during a certain period of day or night, it is active during both night and day with short periods of sleep and activity.
You can read more interesting facts about gerbils here.