Some of our region’s mammals and birds either hibernate or migrate to survive the cold winter season of limited food resources. Snug in dens, they snooze through the cold weeks and months or fly thousands of miles to tropical regions full of insects and blooming flowers.
Many other animals are still visible during the winter, finding shelter among conifer evergreens and foraging for grasses, seeds and berries. Our carnivorous predator animals, such as coyote and fox, rely on smaller prey animals for survival, as do raptors, such as hawks and owls.
What about our aquatic and terrestrial amphibians and reptiles? How does a frog survive when its pond home is frozen solid, and where do salamanders go for the winter? How does a turtle breath under a layer of thick ice, and where do snakes go to escape the cold? The survival of these animals is just as fascinating as the long migration of birds or the winter snooze of woodchucks and chipmunks.
Unlike warm-blooded mammals and birds, amphibians and reptiles are cold-blooded and don’t generate their own body heat. They are living thermometers and their body temperatures mirror that of their environment, making winter a great challenge for survival. They need to hibernate and somehow keep warm to prevent freezing to death.
During warmer months, frogs breathe through their lungs and we’ll see them with the tip of their head and nose just sticking up out of the water to take in air, or out of the water sunning themselves on a log or edge of the pond . But in winter, when the surface of the pond is frozen over, they snuggle down inside the mud to avoid freezing and rely on an amazing ability to take in life-giving oxygen through their skin.
Turtles also burrow into the mud and absorb some oxygen through their skin, mouths and cloacae. The cloacal opening is the anus. During winter months, when the turtle’s body functions slow down, the cloaca widens to allow water to circulate into the opening. Like gills of a fish, the circulating water provides oxygen, which is absorbed by the many capillaries located in the cloacal opening.
Painted turtles can hibernate for months in low oxygen levels (hypoxic) and even no oxygen (anoxic) environments. For most vertebrates, heart and nervous systems fail without oxygen, making the painted turtles’ hibernation somewhat amazing.
Painted turtles reduce their metabolic rate by as much as 95% with access to oxygen and as much as 99% when there is no oxygen available. This low metabolic rate prevents them from being active but also reduces their energetic needs to a bare minimum, allowing them to survive without food or oxygen.
Our terrestrial amphibians and reptiles are equally as challenged by the deep cold of winter to survive. The winter survival of wood frogs is amazing in that they literally freeze, and yet somehow emerge in spring like frog zombies returning to life. They hide during winter among leaf litter and produce a special anti-freeze in their blood made of glucose and glycogen. This wood frog anti-freeze is taken up in their cells, preventing the formation of ice crystals and certain death. They completely stop breathing and their hearts stop until warming temperatures of late winter and early spring slowly reduce anti-freeze production, literally bringing the small frogs back to life.
Terrestrial salamanders are numerous, but you need to work to find them. Rolling over a rock or log is a good way to find smaller salamanders like the red-backed, considered one of the most abundant vertebrates (backboned) in the northeast. Others like the spotted salamander live underground during most of the year and emerge in early spring to mate and lay eggs in vernal pools and shallow ponds. The eggs hatch and within a few months metamorphosize from breathing with gills to lungs and the salamanders leave their aquatic nursery for a life underground.
During winter, salamanders will seek out burrows deep within the soil and leaf litter and below the frost line. Like other coldblooded amphibians and reptiles, they enter a state of brumation, but unlike the deep sleep “torpor” of mammals during hibernation, will wake from time to time.
Snakes also seek out burrows under the frost line, but unable to dig, may rely on crevices between rocks, typically using those facing south and east for heat retention. Snakes also appropriate dens of woodchucks, chipmunks and other animals and will congregate together to share winter quarters, even curling up together to help retain moisture. Their metabolic rate decreases and body temperatures drop to 35 to 45 degrees. Snakes may return to the same winter each year.
At this writing, we have had three consecutive mornings with heavy frosts. Many of the deciduous trees have already lost all their leaves with only the stately oaks and hickories still holding fast to their yellow and brown foliage. Our aquatic and terrestrial amphibians and reptiles are on the move to their winter homes. With the snows of winter, I’ll be thinking of them and their amazing ability to survive.
We live in a beautiful place called The Last Green Valley. Every day is to be cherished. Each sunrise brings a new opportunity to explore. Every sunset is a reminder to enjoy it, care for it, and pass it on.
Information for this column was gleaned from the Stokes Nature Guide to Amphibians and Reptiles by Thomas F. Tyning, the Stokes Nature Guide to Observing Insects by Donald Stoke, Massachusetts Audubon, Connecticut Department of Energy and Environmental Protection, and other sources.
Bill Reid is the chief ranger of The Last Green Valley National Heritage Corridor and can be reached at [email protected] or by calling 860-774-3300.