On The Trails: Flying squirrels
- Mary F. Willson
- 7 hours ago
- 3 min read
By Mary F. Willson
A rather common but seldom seen denizen of our forests is the northern flying squirrel (Glaucomys sabrinus). They are strictly nocturnal and rather small (about the size of our more familiar red squirrel).
This species ranges from interior Alaska and the Yukon to California and Colorado in the western U.S., and all across Canada and the northern states to the East Coast. Within that broad geographic range, a number of subspecies occupy different regions. Even within Southeast Alaska, there are several genetically distinct populations. (Another species of Glaucomys lives in eastern North America; the Old World flying squirrels are in a different genus).
They usually favor continuous mature coniferous forests or mixed forests with good, large patches of big conifers. Each squirrel has a home range of at least several acres, sometimes 80 acres or more. Within a home range a squirrel has several dens; they often change dens fairly frequently and often share a den with others, especially in winter. Dens are often in tree cavities or witch’s brooms, sometimes in old bird nests, or in the ground, or in their own leafy nests (dreys).
Despite their name, these squirrels don’t fly. They glide. Stretched between fore and hind leg on each side is a wide membrane (the patagium). By spreading out all its legs, the squirrel spreads the patagium. The foreleg is elongated and there is a special cartilage on the wrist that helps control the patagium. That makes possible a controlled descent; the direction of the glide can be changed by moving the legs to change the shape of the patagium and the tail can act as a rudder. The squirrel takes off from high on one tree trunk, glides down to another trunk and lands head-up; the spread patagium softens the landing. The squirrel then scampers up that trunk. Most glides are less than a hundred feet long, but exceptional glides may reach 300 feet or so. It may make several glides in succession, and a squirrel can travel a mile or more in an evening.
The breeding season is in spring, but the timing within that season is variable — breeding is later after long, severe winters. Females gestate for a bit over five weeks and in Alaska usually produce two offspring, although litter size is commonly larger elsewhere in the range. Offspring depend on maternal lactation for nine or 10 weeks; at about three months they learn to glide and can forage for themselves, becoming independent of the mother. At seven or eight months they reach full size and commonly are sexually mature, ready to breed, when about 11 or 12 months old. But the lifespan is quite short; annual mortality is high and most of them don’t live longer than about four years.
Flying squirrels are omnivorous. Unfortunately, there are few data specifically for Alaska and for Southeast in particular. Over the whole geographic range, the diet is highly variable: fungi, lichens, fruit, green vegetation (including spruce tips), tree buds, nuts and seeds, insects, carrion, bird eggs and nestlings. They are well-known as important dispersers of truffle spores — they dig up and eat the underground fruiting body of those fungi, dispersing the spores in their feces.
They are prey to owls, of course, and also to small carnivorous mammals, including marten and foxes.
Their fur has an interesting and unusual feature: it is fluorescent (pink!) under strong UV light. That raises the question of possible adaptiveness. Is that fluorescence itself somehow useful — and if so, how? Alternatively, perhaps that is just a side effect of some chemical interactions within each hair that has some utility (still to be understood). The curious naturalist would love to know!
• Mary F. Willson is a retired professor of ecology. "On The Trails" appears periodically in the Juneau Independent. For a complete archive of Mary Willson’s “On the Trails” essays, go to https://onthetrailsjuneau.wordpress.com
