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NATURAL HISTORY

SAN BERNARDINO FLYING SQUIRREL } Glaucomys sabrinus californicus
FAMILY: Sciuridae

DESCRIPTION: The San Bernardino flying squirrel is a subspecies of the northern flying squirrel. It is medium sized, grayish brown, and distinguished by the furry, parachute-like panels of skin that stretch from wrist to ankle, allowing it to glide between trees. Flying squirrels are active at night and are known to glide for distances of more than 300 feet.

HABITAT: The San Bernardino flying squirrel lives in high-elevation, mixed-conifer forests dominated by Jeffrey pine, white fir and black oak between 4,600 and 7,550 feet. Flying squirrels thrive in forests with big trees and closed-canopy cover, large snags that provide nesting cavities, downed logs that foster the growth of the truffles they eat and understory cover that provides protection from predators.

RANGE: The historic range of the San Bernardino flying squirrel lies within the San Bernardino and San Jacinto Mountains of San Bernardino and Riverside counties in Southern California. However, this subspecies appears to be extirpated or near extirpated from the San Jacinto Mountains, with the last anecdotal sightings recorded in the 1970s and 1980.

MIGRATION: The San Bernardino flying squirrel is restricted to the upper-elevation forests of the San Bernardino Mountains, and unlike as with most other flying squirrel subspecies, geographic barriers prevent it from moving to other regions. It is isolated from flying squirrel populations to the north by 150 miles of Mojave Desert, to the west by the Cajon Pass between the San Gabriel and San Bernardino Mountains and to the south by the Banning Pass between the San Bernardino and San Jacinto Mountains.   

BREEDING: Although little is known about the San Bernardino flying squirrel’s breeding biology, other northern flying squirrels produce one litter of two to three young in spring or summer. Females give birth and care for their young in maternal dens made in tree cavities or leaf nests. Babies are born hairless with closed ears and eyes, and eventually leave the nest at two months old. The northern flying squirrel has a comparatively low reproductive rate for a mammal of its size.

LIFE CYCLE: No data is available on the San Bernardino flying squirrel’s life span; however, the maximum lifespan for other northern flying squirrel subspecies ranges from four to seven years.

FEEDING: Flying squirrels spend considerable time foraging on the forest floor searching for truffles, the underground fungi that are its primary food. They detect truffles by digging near downed logs where the fungi are often abundant, smelling the truffle’s distinctive odor and remembering good foraging locations from prior years. Flying squirrels play an important role in maintaining forest health by dispersing truffle spores; truffles form beneficial symbiotic relationships with trees and plants, helping them absorb water and nutrients.

THREATS: The San Bernardino flying squirrel is threatened by rising temperatures and increasingly frequent droughts resulting from climate change. As temperatures warm, high-elevation conifer forests in Southern California have been moving upslope, shrinking the squirrels’ habitat. Droughts threaten the squirrel’s food supply of truffles, which require moist, cool forest conditions. The squirrel also faces threats from forest-management practices that remove canopy cover, snags and downed logs, degrading the squirrel’s habitat; and ever-increasing urban development in its mountain home.

POPULATION TREND: The San Bernardino flying squirrel is thought to be extirpated or near extirpated from the San Jacinto Mountains. Population size and trends for the remaining flying squirrel population in the San Bernardino Mountains are unknown; however, low densities of squirrels estimated in the 1990s suggest that it is not abundant.

Northern flying squirrel photo © Brad Barrett