The following appeared in the January 2014 issue of Jefferson County Observer (WV).
Winter Survival Secrets
This season is a life-or-death challenge for local wildlife.
Some species escape the cold and deprivation via migration, but the majority who
live here must weather in place. The
strategies of warm-blooded mammals and birds contrast with those of reptiles,
amphibians and insects who can't internally regulate their temperatures But all
have intrigued generations of naturalists. Grab your coat and join me on a
search for some animal survival secrets.
The silhouette of a drey
is easy to see high in the bare branches of that black walnut tree. In early fall, a gray squirrel gnawed off slender
twigs and vines with green leaves still attached. She wedged these materials
between the branches, weaving them into a rough sphere with a hollow center.
She lined the interior with soft materials such as pine needles, grass and moss.
Squirrels mate twice a year and give birth in June and January, so its possible
that two or three squirrel pups are nestled inside with their mother. Gray squirrels
do not hibernate--they hole up during the worst days of winter. Dreys provide shelter in landscapes where
tree cavities are scarce.
In the grassy bank next to the meadow, we can see the
entrance to the burrow of one of our resident groundhogs. Also known as a
woodchuck or whistle pig, ground hogs are true hibernators. A groundhog binges
all summer, then enters an extended period of lethargy while living off its fat
stores. Its heartbeat slows from 80 beats per minute to less than 5, and its
temperature can drop to as low as 38 degrees Fahrenheit. In February or March,
it will reappear with a much slimmer figure.
Here in this overgrown shrubbery is an abandoned bald-faced
hornet nest that appears to be constructed of papier-mâché. Hornets are a predatory social wasp. Through the warm months, a single hornet queen
and her female workers fashioned the nest from wood pulp mixed with their saliva.
When temperatures started to cool, the
colony produced fertile males and females. After mating, only the fertilized
females survived, the rest of the colony died.
These new queens sought refuge in small crevices--perhaps
beneath the bark of a rotting log or under the siding of a shed. A substance in their bodies
called glycerol will help them resist freezing. When warm temperatures return, the
queens will revive from their state of dormancy, seek out new sites to colonize
and begin another season of nest building. The multiple layers of this old nest
now provide a winter home for other insects and spiders.
Certain plants are associated with the reproductive cycles
of particular species of butterflies. A survey of what was growing here gives
clues to the presence of caterpillars in a suspended phase of development known
as diapause. After last season's
violets wilted and died, an adult female Fritillary butterfly purposefully laid
eggs in this shady spot. The larvae hatched and burrowed into the earth. When
the new violet plants emerge, the caterpillars will awake to feed and continue
their life cycle.
When in blossom, the pollinator garden was alive with scores
of nectaring butterflies. Today withered flower stalks stand still and silent. It is good that their remains are left undisturbed.
Tiny Silvery Checkerspot caterpillars may be hibernating at the base of the
coneflowers and Pearl Crescent
We find the pond rimmed with ice. Despite the most frigid winter, the bottom of the pond is
unlikely to freeze. The pond's depth is below the frost line. As water
approaches 32 degrees Fahrenheit, instead of becoming more dense and sinking to
the bottom, it expands and rises. This
property of water provides an advantage to aquatic turtles and frogs.
Painted turtles who lolled in the sun here several months
ago are now submerged in the mud. They
have slowed their body processes to where they can exist on the smallest amount
of oxygen or even survive periods of no oxygen at all. Since it is impossible
to breathe through their lungs while underwater, the turtles have evolved the
ability to take in oxygen from the water through blood vessels in the throat
and special tissues near the tail.
The
bullfrogs that live here are also submerged for the duration but obtain oxygen
from the water through their skin. They bury
themselves only partially or simply lie on top of the mud. From time to time
they stretch their legs and swim about in slow motion.
What about the
land frogs and toads? Some of them, like
the American Toad, can burrow deep into the ground, evading the most deadly
temperatures. Other species that lack such digging ability, must settle for
whatever crevices they can find or crawl beneath the leaf litter. These are
inferior shelters when the mercury plummets. Somewhere nearby may be a
partially frozen Wood Frog, no longer breathing, its heart stilled. If we
unearthed its hiding place, it would appear dead. The frog's vital organs resist freezing due
to a high concentration of glucose. When this cold spell is over, the frog's
frozen portions will thaw, and its heart and lungs resume activity.
The wind is
picking up--time to think of our own survival. Let's gather a few sticks from
the woodpile on our way back. As we
rattle the tarp, we hear the skittering of a field mouse. By removing a few layers of wood, we can take
inventory of its nest materials: grass, wood chips, bits of fur--and surprisingly,
scraps from a cast-off snake skin. The stacked wood creates a honeycomb of insulated
compartments ideal for small inhabitants. Perhaps the snake that preys upon the
mouse and her kin also chose this site for its winter refuge chamber or hibernaculum.
There is no
activity at the bird feeders this evening. The Tufted Titmouse has fed well today
on the black oil sunflower seeds and has found a miniscule pocket of shelter somewhere.
The abundant calories will fuel its body
heat through the dark hours. There can be extra warmth in numbers--perhaps
several of the birds have jammed their bodies together in one tiny space. If
you see a Titmouse with a crooked tail on an icy morning, it tells of a cramped
but effective sleeping arrangement.
Our walk is at its end but has only begun to scratch the
surface of winter survival secrets. As night falls, snow drifts down, adding a blanket
of protection to all the living things that slumber beneath.
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