Small squirrels, shrinking habitat
In learning about a species, often start down what appears to be a simple path leading to a mundane life, only to be drawn into a much more complex world with fascinating interconnections. I began such a journey recently when Larry Sherertz sent me some flying-squirrel photos he’d taken.
Flying squirrels are “incredibly fast and frenetic” and “ridiculously cute,” as Larry aptly described them. Being nocturnal, they have huge eyes to help them navigate in the dark, and they do what no other mammal in North America can do — glide through the air, thanks to membranes connecting to their front and hind feet on each side. They are so agile in flight that they can actually do a 180-degree turn in midair.
Although often outnumbering gray squirrels in some areas, the flying squirrels’ secretive, nocturnal lifestyle and preference for living high in forests means that they are rarely seen by humans. They will sometimes take up residence in our attics, in which case we may hear them. And they will sometimes visit houses at night if someone leaves a few seeds and nuts out for them, as Larry does.
There are two species of flying squirrel in North America — the southern ( Glaucomys volans) and the northern ( Glaucomys sabrinus). The southern species, which is quite common throughout the eastern U.S. at elevations below 3,200 feet, is a little more than 5 inches long, with a 4-inch tail. It eats a wide variety of seeds, nuts and buds and, according to the Virginia Fish and Wildlife Information Service (VaFWIS.org), is also the most carnivorous squirrel in North America, dining on insects, baby birds, eggs and even carrion.
A bit bigger and browner than its southern cousin, the northern flying squirrel is quite common north of here, but in the Appalachians of Virginia, West Virginia and North Carolina — the southernmost part of its range — it’s mostly found above 3,500 feet. It has evolved to have a more specialized diet than the southern flying squirrel, preferring food found in redspruce ( Picea rubens) forests, which threatens the northern squirrel’s survival this far south.
These forests, which here occur only at high elevations on cool, damp, north-facing slopes, are rapidly disappearing — only 2 percent remain, says naturalist Ron Hughes, a lands and facilities manager for the Virginia Department of Game and Inland Fisheries. In the 1990s, as a graduate student, Ron participated in a study of the Carolina flying squirrel ( Glaucomys sabrinus coloratus), which, along with the Virginia version ( Glaucomys sabrinus
fuscus), are the subspecies of northern flying squirrel inhabiting the southern Appalachians.
The loss of such highelevation boreal forests “has been incredibly fast,” Ron says, making them second only to the Everglades as “the most threatened habitat on this continent.” Their destruction is mostly from human activity, including mining through mountaintop removal, logging, ridge-top development, introduced insect pests, acid rain and climate change.
Through the increasing isolation of populations on high-elevation habitat “islands” at the southern end of the northern flying squirrel’s range, it has evolved into 28 subspecies. The southern flying squirrel, by contrast, lives in areas that overlap more, and has evolved into only four subspecies. In Virginia, forest destruction has marooned the northern species on habitat islands in four counties, according to VaFWIS: Highland, Montgomery, Grayson and Smyth.
While the northern flying squirrel may supplement its diet with seeds, fruit, meat and buds, the “mainstay” of its diet are truffle-like fungi in the genus Elaphomyces, which are associated with red-spruce forests, according to an article in the May/June issue of “Nature Conservancy Magazine” (magazine.nature. org).
The fate of the squirrel is entwined with that of the red spruce and the fungi through a complex symbiotic relationship. Basically, the fungi are mycorrhizal, living underground and attached to the trees’ roots. They help the trees break down and take up nutrients and water and protect the trees’ roots from harmful fungi and nematodes. Because the fungi are underground, they rely on a specialist like the squirrel in order to reproduce and spread. The squirrel eats the fungi, dispersing their spores when it defecates.
Some researchers, including Ron, say the symbiotic nature of the squirrel’s relationship to the fungi may mean it’s a keystone species of the red spruce forest ecosystem — if the squirrel disappears, the forest could also. The fungi make up the major portion of the squirrel’s diet — up to 98 percent in the Pacific Northwest, according to one study. Ron adds that the squirrel’s diet can be more varied in the southern Appalachians.
In the study of the Carolina flying squirrel in North Carolina, the study area was similar to those of high-elevation red spruce forests, but the forest there was almost devoid of conifers, Ron says. So what were the squirrels eating? Ron suggests it may be different mycorrhizal fungi that are associated with ericaceous shrubs, which were also in the study area, including laurel, blueberry and rhododendron. He adds that more research on the squirrel’s diet is needed.
The lack of suitable fungi at lower elevations in the southern Appalachians — and the northern flying squirrel’s vulnerability to predators, parasites and diseases there — will likely keep the squirrel at high elevations, threatening its survival there, Ron says. The Carolina flying squirrel and the Virginia (aka West Virginia) variant, which are the only subspecies found in Virginia, are listed as endangered on state and federal lists.
“Their plight in the Appalachians started when humans started to destroy all the spruce forests,” Ron explains. These forests depend on a rich substrate of humus to survive. In return, the trees provide shade and slow runoff, which protects the substrate. Once the trees are removed, Ron says, the peat- like substrate dries out and fires are more likely to occur, destroying it forever, along with the spruces’ seeds.
While the southern and northern flying squirrel species, “do not like each other,” according to Ron, their ranges can overlap a bit at higher elevations. There, they will often use the same nesting sites, including woodpecker holes, or the former nests of birds and other squirrels. This has led to a further stressor on the northern species: An intestinal nematode carried by the southern species that has little effect on that carrier but kills northern flying squirrels, according to a January 2010 article in the “Journal of Wildlife Diseases.”
While only the southern flying squirrel is likely to be spotted in Rappahannock these days, “until pretty recently there were probably northern flying squirrels in Shenandoah National Park,” Ron says. Although surveys for them done around Hawksbill Mountain did not turn up any evidence, “I bet you that a pretty good percentage of the park above 3,200 feet elevation had spruce on it,” he adds, basing this on the remnant balsam fir trees that are still there.
While several conservation organizations and government agencies have united in West Virginia to reforest areas where red spruce has been destroyed so northern flying squirrel populations can rebound,, Ron says no such effort is underway in Virginia.
Although leaving out bird feeders can attract some very unwelcome visitors, a bit of seed left out here in Rappahannock can attract a common yet rarely seen nocturnal denizen of Virginia’s forests, the southern flying squirrel.