They feed on a variety of plant material as well as tree sap, fungi, insects, carrion, bird eggs and nestlings.

Fish and Wildlife Service temporarily put the West Virginia northern flying squirrel back under protection on June 6, 2011, in response to a court order.

Fish and Wildlife Service to give the San Bernardino flying squirrel protections as an endangered species, but ultimately their request was denied.

Fish and Wildlife Service said, "in a thorough status review of the species using the best available science, the Service has found that the squirrel is abundant where it is found and that the threats to habitat loss from urban development, habitat fragmentation, wildfire, urban air pollution and climate change do not pose significant threats to its long-term survival.".

[8] The Center for Biological Diversity argues that temperature changes are reducing the San Bernardino flying squirrel's forest habitat and negatively affecting the availability of the truffles it feeds on, with urban development impacting the area as well.

The adult northern flying squirrel measures from 25 to 37 cm long, and their weight can range from 110 to 230 grams.

[2] Once in the air, they form an "X" with their limbs, causing their membrane to stretch into a square-like shape[2] and glide down at angles of 30 to 40 degrees.

[3] Just before reaching a tree, they raise their flattened tails, which abruptly changes their trajectory upwards, and point all of their limbs forward to create a parachute effect with the membrane to reduce the shock of landing.

[2] The limbs absorb the remainder of the impact, and the squirrels immediately run to the other side of the trunk or to the top of the tree to avoid any potential predators.

[2] Although graceful in flight, they are very clumsy walkers and if they happen to be on the ground in the presence of danger, they will prefer to hide rather than attempt to escape.

[10][3] A major food source for the squirrels are fungi of various species, although they also eat lichens, all mast-crop nuts, tree sap, insects, carrion, bird eggs and nestlings, buds and flowers.