Winter in Tennessee…what images
come to mind? Short days, cold nights, bright stars, barren landscapes,
ice and snow…decay…and death? Sure, the bounty of fall
colors is just a memory, the animals have fallen silent, all is
a still, slumbering, shivering senescence. Right? Well, not exactly.
Sure, our neotropical
migrants have returned to equatorial or southern hemispheric habitats,
most of the frogs have burrowed into the mud for a respite, and
Smokey Bear has locked his shovel in the tool shed. But to think
that the party that is biodiversity in Tennessee is over is far
from the truth. Look around, look down, look under. Dig deeper.
Winter may be a time
when Tennessee’s myriad botanists can slow down a bit (not
like they ever have to move very quickly anyway) to examine
all the specimens they pressed in the preceding months. Zoologists
are not necessarily so fortunate (depending on your propensity for
sticking bare hands in to 30-something degree water!) A number of
our more interesting native animals do their "thing" about
as much in winter as they do the rest of the year, if not more so.
But where are they, "if’n" we can’t see them?
Well, outside of what
flies to your feeder, or steals food out of your dog’s bowl
at night, they are pretty much underground or underwater…places
that are not likely to freeze (too much) even in the still of winter.
While working as the
zoologist with the Natural Heritage Program, I have had the pleasure
of seeing some of our most interesting creatures in places where
the sun don’t shine. An easy way to look at our winter occupants
is topographically. There are those that are near the soil surface,
under rocks or dead leaves, for instance; those that favor aquatic
habitats, including surface streams, lakes, ponds, and even temporary
puddles; and those that live underground, as in caves, sinkholes,
or groundwater- just in winter, or in some cases, year-round.
Let’s start up
on top and work our way "way down under":
Terrestrial Inhabitants
Now I don’t expect
the readers of this magazine would appreciate my rambling on about
every soil microbe that can be found in Tennessee dirt, nor would
I pretend to want to write such a tome. Certainly, though, a number
of our wingless wonders of winter do deserve mention- animals that
s-l-o-w down more than they do actually hibernate (like Smokey).
Such species are known
as ectotherms- animals whose body temperature depends almost wholly
on that of the environment. Many of our ectotherms are familiar
to you, especially if you have ever fished with live bait or kept
a garden…worms, slugs, pill bugs, beetles, and the like…but
other Tennessee species may be spied (or spy you) even on warm,
sunny winter days.
The common Eastern Garter
Snake (Thamnophis sirtalis), a resident of urban, suburban,
and rural habitats, can occasionally be seen foraging about or basking
in the sun.
Many ectotherms can
only digest food if their core body temperature reaches a minimum
temperature…compare that process to how difficult it can be
to flex your hands on a very cold winter day, and you get the idea.
Since garter snakes
are communal burrowers, you may find more than a few out on that
unexpectedly warm winter’s day. Of course, being up, warm,
and active may mean little if there is nothing to eat, so this strategy
has its risks. But, if food is available, such as various invertebrates
(okay, okay, "the early bird gets the worm"), then
this wintertime activity can prove very helpful in keeping reserves
of body fat and energy for those days that are nasty, dark, and
cold.
As an aside, another
Tennessee ectotherm, the Wood Frog (Rana sylvatica) has evolved
to have its own built-in antifreeze…exceedingly high concentrations
of glucose in the bloodstream (talk about a rush!).
As days grow short,
cool, and dark, a Wood Frog’s physiology kicks in to flush
its tissues with this sugar, so that the freezing point of its blood
is depressed below 32 degrees Fahrenheit.
This means these amphibians
can "hibernate" relatively close to the soil surface (under
leaf litter) without fear of forming ice crystals in its body, which
would most likely be lethal.
Being close to the surface
also means that they will rapidly sense when the world above has
warmed enough to get "officially" active for the new year.
It is no accident that the Wood frog is, without fail, the first
frog to emerge and begin breeding each new year…in some places
starting in January (oh, those intrepid Capricorns!)
Not to belabor the amphibians,
but the Spotted Salamander (Ambystoma maculatum) is another
early riser, meaning they also stay reasonably close to the surface
in winter, just in case a warm rain should come and fill up the
temporary woodland pools they use for breeding.
Look for the Spotted
Salamander in late winter, on rainy nights that signal them to move
to breeding ponds or puddles, or look for their aftermath- large,
firm egg masses in still waters in or adjacent to the forest. Sometimes
their egg masses can be as large as a toy football-and almost as
firm to the touch. Not surprisingly, you can find their eggs in
or near the same habitats where Wood Frogs are making lots of noise!
Among the endotherms
(warm-blooded) animals active in winter, the voles may be some of
the most noticeable.
Often mistaken for a
popular athletic program, the Tennessee Voles can be counted on
to keep ground surface just a little bit more habitable than it
otherwise might be.
How? Glad you asked.
Voles (not moles) are rodents (genus Microtus), and as such
have a propensity for making tunnels in the dead grasses and leaves
which become a ubiquitous part of the Tennessee landscape in winter.
Duck and goose hunters
have probably noticed their handiwork while traipsing across an
old field on the way to the blind…turn back a tuft of grass
and you can just about bet you will see a cross-section of a tunnel
or maybe even a nest.
One benefit of tunneling
as they do creates a pocket of air that may be both warmer than
the ground beneath and warmer than the air above. The thermal
benefits for the voles, mice, and other creatures must be remarkable,
since these rodents seem so prosperous and populous!
Such a blanket of tufted
grass absorbs radiant energy from the sun (and not just on sunny
days!), holds the heat (think of the insulation in your house),
and back-radiates it slowly into the ground-keeping all manner of
winter tenants happy.
Aquatic Creatures
Fish. There, I said
it. And no, I don’t have space to talk about all of them, either!
Suffice to say that Tennessee has over 270 species of fish, all
of which (so far as I know) don’t sleep off the winter.
Sure, they slow down,
don’t eat as much, but boy, can they drink!
But rather than tackling
our scaly friends (which a few other magazines target), I would
like to introduce you to another ectotherm, affectionately known
as bait to many fishers.
That’s right- crayfish,
or crawdads- our very own decapod crustaceans- which number over
70 species in Tennessee.
I have had the thrill
of working with a few ‘dads since coming here (and not in etouffee,
mind you), one of which deserves special mention in our "Winter
Olympics."
Nashvillians (and regular
folk, too) will gladly tell you things for which our city is famous…the
Cumberland River, the Hermitage, a bustling economy, that-other-university-that-isn’t-U.T.,
and the most recognizable of all Nashville symbols, that for which
we are known the world over-the Nashville Crayfish- Orconectes
shoupi.
Known only from the
Mill Creek basin in Davidson and Williamson counties, this little
giant put the "twang" in the Music City long before Timothy
Demonbreun started trapping the area. In fact, if ever he dined
on crayfish out of Mill Creek (the mouth of which is very near the
cave that bears his name), you can bet he ate a few of these in
a pinch.
So what makes this creature
so special? For starters, Mill Creek is the only system in which
it naturally occurs. It is found in the mainstem of Mill Creek,
numerous large tributaries, and even some small second-order streams
that eventually flow into the creek.
Because of its limited
distribution and threats from continuing development of the Mill
Creek watershed, the U.S. Fish & Wildlife Service listed the
species as "Endangered" in 1986. The Tennessee Wildlife
Resources Agency followed suit and listed the species "Endangered"
under state law. O. shoupi remains the only federally listed
crayfish species in the State of Tennessee, and is darn proud of
it.
But what makes winter
such an important time for the species? Well, to answer that question
you have to know a little anatomy as well as ecology.
Starting with the latter,
it is important to note the role (niche) of crayfish as the "garbage
men" of the stream environment. Crayfish are often directly
responsible for converting dead animals, plants and coarse woody
debris (CWD) either into smaller particles ingestible by other organisms
or into digested waste matter on which other organisms feed.
Beginning the decay
of the tons of leaves that enter Mill Creek each fall is an important
contribution of its crayfish, and Nashville crayfish are providing
this service year round, without charge (try to get your
leaves picked up for free!)
The Nashville crayfish,
as a dedicated stream-dweller, is sleek and built for speed. It
lives primarily under slab rock in areas with relatively little
sediment (a precious commodity in Mill Creek!). From these watery
haunts the species emerges to forage and feed primarily at night.
As a member of the genus
Orconectes, the species is recognized as a non-burrowing
crayfish (e.g. it doesn’t make "chimneys" or tunnels
as some species do). To distinguish this species from other closely
related (and similar looking) Central Basin Orconectes, one
has to examine several anatomical features: O. shoupi has
elongate pincers with red tips, a black band around each, and a
light "saddle" on its carapace (back).
Crayfish taxonomists
learned long ago that color and patterning was often not enough
to distinguish species- a more intricate and intimate character
was needed!
All the useful crayfish
keys are therefore based on the first pleopod (gonopod) of male
crayfish- a.k.a. their reproductive organ(s). Males of any of the
70-plus Tennessee crayfish species have a pair of these organs tucked
underneath their hind legs. The structure of these organs, however,
is unique to each species. And that makes identification possible,
if not downright fun (but not so much for them).
Crayfish molt their
exoskeleton at least twice per year, both into and out of a breeding
molt. Typically, males molt into breeding condition in the fall
(Form I), and the gonopods take on the characteristic shape which
they maintain throughout the winter.
Courtship and breeding
occur in fall and early winter, and females deposit eggs under their
tails in late winter and carry them until they hatch in the early
spring. The young actually stay attached to the female for some
time, completing their first stage of growth in her protection.
They then drop off and distribute themselves across the creek, stream
or lake bottom. In spring, males molt out of breeding condition
and into Form II, the non-breeding or juvenile form.
So, if anything, winter
is probably one of the most important periods for this species,
in that it is the time of year that determines, in part, the abundance
of the following spring’s young.
If, in your winter romps
in Tennessee creeks, you should spy a slow-moving crayfish and pick
it up, don’t be surprised to find hundreds of little ones sticking
close to mom through the darkest days of the year!
Dark and Loving It
Wintertime life in the
soil...in the waters…and in the caves, too! Despite the scarcity
of such features in West and far East Tennessee, the limestone-rich
regions of the state (Highland Rim, Central Basin, Cumberland Plateau,
and Ridge & Valley) are blessed with over 8,000 documented cracks,
caves, and crevices.
As these features have
developed over the eons, so have creatures adapted to cold, low-nutrient,
dark (or nearly so) conditions moved in to exploit them.
Think of it- a place
(at least on the subsurface) that seems so foreboding, so dangerous,
that few other species would dare call it home- you could have the
whole place to yourself.
Well, our caves are
not nearly so bleak, zoologically speaking (okay, I will admit that
not too many botanists can claim they go caving for work-related
reasons…with one notable exception - see quiz below). Tennessee
is again blessed with an abundance of species that are either cave-obligate
(gotta have ‘em; a.k.a. troglobytes) or cave-facultative (love
‘em or leave ‘em; a.k.a. troglophiles).
Such taxa include our
native (and cute) Eastern Woodrat, several bat species, both common
and rare, at least four species of blind crayfish, one eyeless fish,
beetles, spiders, flies, moths, and (depending to whom you speak)
potentially four species (or sub-species) of cave-adapted salamanders.
Our true caves (having
a minimum 50-feet vertical or horizontal passage) have generally
one thing in common- constancy of environment- when compared to
the surface, at least.
Dry caves, wet caves,
upper and lower passages, tubes, fissures, cracks, sumps, domes…all
the features that draw cavers underground…can all be expected
to hover around 54-56 degrees Fahrenheit all year. It can be 105
outside, but a comfortable 50 degrees cooler just a few feet down.
When you and I are slogging through 24-inches of "partly cloudy,"
cave critters are just hanging around paying us no never-mind.
Still, winter is one
of the most important seasons for cave species. Bats that over-winter
in caves, ostensibly hibernating, use this time to conserve stores
of body fat during a time of year when their prey (flying insects)
is relatively absent from the surface.
Winter is the time when
pregnant bats are gestating their young- typically giving birth
to only one pup per year, the following spring.
If you should come upon
hibernating bats while caving in the winter, please leave them be
and quietly exit the area. Hibernating bats can actually starve
to death if they are roused in the winter at a time when no prey
is available.
But other cave species
are quite active in the winter. The Southern cavefish (Typhlichthys
subterraneus), and blind cave crayfishes (Orconectes pellucidus,
O. australis, O. incomptus, Cambarus hamulatus) go right on
about their business as though the seasons had not changed. For
them, that is probably the case. So, their activity patterns (breeding
season, for instance) are determine less by clues which we accept
as indicating changing seasons (like leaves falling), but more by
an internal clock or in some cases, subtle changes in water chemistry.
One of our rarer rodents,
the Eastern Woodrat (Neotoma magister), is active. All winter
woodrats are infamous as pack rats (not unlike their European cousins
found in Tennessee cities), typically occupying the transition (twilight)
zone in caves - that area, which is truly neither cave nor surface,
and into which at least some light penetrates.
Woodrats forage for
food and nest material near the entrance of caves year-round, but
put up winter stores especially in the fall (nuts galore!). They
will collect bits of trash, metal, or shiny objects as well, and
add that to their perched nests. It is even possible to get a rough
estimate of human cave visitation by examining the amount of trash
they bring in each year. That is to say, they do a pretty good job
of cleaning up after ourselves!
So, whether they bask in the sun,
dig tunnels for fun,
Or crawl through the night-while water's
in sight,
To surpise a new friend,
With a pinch in the end
Of a fine winter's day...
Our coy comrades are
still busy at a time of year when many of us "topside"
figure that everybody is taking a long nap between fall and spring.
Certainly that is far from the truth in the Volunteer State. This
winter, forget the comfortably numb pursuits of winter's deep -
the Super Bowl, the bowl games and the like and take a Tennessee
hike on a wintry day.
Wintertime is just about
the best season to find quiet and solitude in our countryside, and
if you are lucky, and willing to look a little bit, you might just
find a Tennessee creature willing to share some of that with you.
Be sure to give it right back.
For more information,
contact the Division of Natural Heritage at 615-532-0431.
Quiz (for land-lubbers):
Can you name a plant in Tennessee that requires botanists to imitate
cavers if they want to observe it? [Hint: only one location is known
in Tennessee, from Marion County.] Winners will receive a copy of
the popular Tennessee Rare Plant List produced by the DNH.
Send your entries to: TDEC, Division of Natural Heritage, c/o Andrea
Shea, 401 Church St., 14th Floor Tower, Nashville, TN 37243-0447
or email: [email protected].
(David Ian Withers
is staff zoologist with the TDEC Division of Natural Heritage in
Nashville.)
