Monday, November 10, 2014

Winter Survival Secrets

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 larvae may be sleeping at the feet of the asters. Not all overwintering butterfly larvae hunker down in the soil.  For example, the Red Spotted Purple larva stays under wraps by rolling itself into a leaf of its host plant, the willow. We might be able to find some of these mini cigar-shapes down by the pond.


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.   






No comments:

Post a Comment