As the cold weather rolls in we cozy up inside, pour a cup of hot chocolate and light up the fireplace, ahh the great advancements of civilization! But what about all the animals? How do they survive the frigid weather of the northeast? Adaptation, migration and hibernation- three key terms to winter survival. Shorter days (photoperiod) as well as a change in temperature trigger a response in animals to prepare for winter; this is hardwired into them as their internal biological calendar. Some responses are obligatory, while others are consequential, but all are quite amazing. Let’s explore a few.
Although hibernation is the common term, it is lesser known that there are few “true hibernators.” This is because while many animals will spend their winter sleeping, not many sleep the whole way through like our groundhog friend “Staten Island Chuck”; instead, they experience torpor or brumation (dormancy in cold-blooded animals). Torpor is a state of inactivity where there is a reduction in the metabolic rate, a lower body temperature and slower heart beat.
When an animal experiences hibernation, torpor, or brumation, they must have additional adaptations to survive these long stretches of inactivity. Many mammals survive the cold season by growing in thick coats of fur, sometimes even slightly changing color to camouflage better in their environments, like the white tailed deer. A white tailed deer’s winter coat is also made up of hollow hairs that trap in air which is warmed by the body. Shrews, voles, chipmunks and white-footed mice will spend much of their time in underground runways and tunnels. Though insects are still readily available for insectivorous creatures, like the shrews, herbivores and omnivores would likely not survive without their caches of food that they have laboriously stored away.
Not all animals live off their larders and caches for the winter. So how do they survive on the small availability of food? Well, many fast for long periods of time; but surviving without food for long expanses is no easy feat. Cold-blooded animals are especially adept at utilizing very little energy, partly because they are not producing their own heat. Garter snakes will gather in the thousands in suitable hibernacula. Other terrestrial reptiles and amphibians will typically seek out deep cracks in logs or rocks or dig below the frost line or into the leaf litter. The wood frog is a spectacular example of adaptation. They produce antifreeze in their system (in this case a fancy term for sugar or glucose), which helps to keep its organs from freezing. The frogs can survive being frozen solid for months on end, during which they have no brain activity and no heartbeat.
Aquatic frogs in a reduced activity state must stay in rich oxygenated conditions, as opposed to aquatic turtles that nestle down into the mud. Snapping turtles and painted turtles can live in anaerobic environments during the winter months. They reduce their metabolism by about 90% and get the little energy they need from stored fat. The lack of oxygen will build up lactic acid in their systems; but their shell will release chemical buffers to break down and store the lactic acid until they have the opportunity to bask in the sun releasing the buildup altogether.
Waterfowl like ducks and geese must forage for food to survive. In freezing water they use their uropygial/preen gland to produce an oil to waterproof their feathers as well as a system called countercurrent heat exchange. Ever wonder how a duck can walk through snow and ice and swim through frigid water without getting frostbite on their feet? The arteries containing warm blood flowing from the heart lay close to the veins moving the colder blood from their feet. This warms up the venous blood and cools down the arterial blood so the temperature difference between the ice and their feet is lessened, reducing heat loss.
Many native animal species, from reptiles to birds to mammals, possess remarkable adaptations that allow them to perform great feats of survival.
By Renee Allen