Fungi, such as mushrooms and truffles, appear to be their most important food source. The seeds of birches and berries are also eaten when in season. For an animal of its small size, flying squirrels can travel quite far, up to 500 metres or more from their nests. Home ranges overlap, so squirrels often forage in close proximity to one another and sometimes can be found feeding in the same place. Flying squirrels' habitats are found in tall trees, snags, decomposing logs and relative understorey, which offer excellent gliding opportunities.
Fungi are more abundant in forests with decomposing logs.
Snags are used for nest sites. These habitat characteristics are generally found in older forests. Since older forests are becoming increasingly rare, flying squirrels are distributed in patches. Northern flying squirrels are very important to the ecology of forests in western North America. Some fungi that they eat form their fruiting bodies underground.