The calls come in all winter, said Paul DeBow of DeBow Wildlife
Service in Plymouth, NH. If there is no snow, the peak will be in
January or February, when it's the coldest. Some people think the
animals they hear partying in the attic are chipmunks, he says. But
they are not.
Chipmunks, DeBow explained, hibernate in winter and what
homeowners are probably hearing are flying squirrels. Because
flying squirrels are nocturnal, few people ever see them.
There are two species of flying squirrels in our area, the
northern flying squirrel and the southern flying squirrel. John
Litvaitis, professor of wildlife ecology at the University of New
Hampshire, said that the southern flying squirrel is the smaller of
the two, often weighing just two or three ounces. "The northern
flying squirrel [at three to five ounces] may be half again or may
be twice as big as the southern," he said.
But even the northern flying squirrel is smaller than a red
squirrel. The southern flying squirrel is about the size of, yes, a
chipmunk (which is a ground squirrel). Both species of flying
squirrels can be distinguished from other squirrels by their
patagium, the membrane between their front and rear legs that
allows them to glide (not fly).
For all their similarities, the northern and southern flying
squirrels are in a conflict that sounds a lot like war. "There was
one paper that was titled something like, 'The South Advances,
While the North Retreats," said Carolyn G. Mahan, professor of
biology and environmental studies at Pennsylvania State University,
Altoona, and a squirrel researcher.
Northern flying squirrels are creatures of conifer (cone-bearing
tree) forests. "We know that northern flying squirrels depend on
fungi that are associated with conifer forests," she said. But
southern flying squirrels can live anywhere. When conifers are
cleared from a mountainside and homes are built, southern flying
squirrels are happy to move in, bringing several more threats to
the northerns. It's not that the two species don't get along; it's
that they get along too well. Squirrels of both species will pile
into the same tree cavity on a cold winter night. Hybrids between
the northerns and southerns follow.
The southern flying squirrels carry an intestinal parasite,
unknown in northern squirrels in places where there are no southern
flying squirrels. Where the two species overlap, the parasite may
be harming the northerns directly, or, as Mahan's research shows,
the parasite may be altering the northern squirrel's internal
ecosystem, allowing other, previously harmless parasites to join
forces with the newly introduced parasite.
The northern flying squirrel is in serious decline in the higher
elevation forests of Pennsylvania, Virginia, West Virginia, and
North Carolina. It is a state-endangered species in Pennsylvania.
The Carolina flying squirrel, a subspecies, is federally
As the many phone calls to DeBow Wildlife Services suggest,
northern and southern flying squirrels seem to be doing just fine
in New Hampshire and Vermont, although it would be hard to tell if
the southerners were overtaking the northerners as they are in
other places. That mystery is the only reason both northern and
southern flying squirrels are "species of greatest conservation
need" in Vermont's 2005 Wildlife Action Plan.
Litvaitis did studies of flying squirrel habitat in the 1990s in
New Hampshire. Southern flying squirrels are dominant along the
seacoast and the southern 20 percent of the state, he said -
basically anywhere you find acorns and hickory nuts. "As you get
inland and northern, it flips to northerns," he said. He assumes
the pattern is similar in Vermont.
One of the more recent studies on flying squirrels done by
Litvaitis' students focused on the animal's energy use. That
patagium, or gliding membrane, exposes a lot of a flying squirrel
to the elements. "Once the temperature got below freezing, they
buddy up," he said, for warmth. "There are real benefits."
That buddying up can mean up to 50 flying squirrels in your
attic during the winter, explained DeBow. "You can't trap them
out," he said. "It's like bailing a leaky boat." Instead, he uses
exclusion, using either a one-way door or a cone that discourages
them from re-entering.
These are the same tools DeBow uses for bats, but when it comes
to control, he likes flying squirrels better for a few reasons. One
is because, unlike the region's disease-decimated bats, flying
squirrels seem to be thriving, at least in the region's attics. He
thinks the popularity of improperly screened ridge vents may be one
The other reason is that they are so boisterous and noisy. DeBow
never has to guess when he's gotten the last flying squirrel to
leave the party.
Madeline Bodin is a writer living in Andover, Vt. The Outside
Story is assigned and edited by Northern Woodlands magazine and
sponsored by the Wellborn Ecology Fund of New Hampshire Charitable