Winter officially begins on December 21; however shorter day-length and cooler temperatures have already triggered the inner timepieces of our local wildlife. Gone from the trails at the Arboretum are the songs of hooded warblers and other migratory birds. Moths and butterflies, which are incapable of flying in temperatures below 40 degrees Fahrenheit are absent from our gardens, except for a hardy-natured bicolored sallow moth here and there. Our volunteer citizen scientists have tracked our three monitored box turtles, each possessing a telemetry transmitter, to the underground burrows they will inhabit until the warm rains of spring return.

Animals have a wide variety of strategies to cope with the coming winter season. These responses are mostly triggered by a lack of food for these animals rather than cooler temperatures. Some of these species and their behaviors are well known to us all, including young children, but there are quite a few species that behave in ways that may be more of a surprise.

Migrating Lower, not South. Warblers and many other neotropical migrants leave their summer breeding grounds and make a long flight to Central and South America for the winter. A bird with a animalhibernation_juncomuch more regional migration route is the dark-eyed junco (Junco hyemalis). These boisterous and active little gray birds are accustomed to life above 4,000 feet in places like Mount Mitchell and Grandfather Mountain in the warmer months, but many find the bitter winds and cold of winter in the highlands less than ideal. Around October we see these birds, particularly females, showing up at bird feeders at lower elevations such as the Asheville region, where they will remain until spring.

Frosty Frogs. Amphibians and reptiles (collectively called herptiles) go through a period of dormancy known as brumation in the winter months. As in mammalian hibernation, herptiles will prepare by storing fat within their body, but they also store up glycogen, a sugar. In wood frogs (Rana sylvatica), this glycogen combines with the frog’s uric acid (a waste product) to act as a sort of anti-freeze that keeps water in the frog’s cells from turning to ice. Amazingly, other than the water within these cells, the entirety of the frog can freeze solid, then thaw and remain a healthy frog. Both mammals and herptiles slow their metabolic processes, but mammals cannot tolerate low-oxygen conditions as salamanders, snakes, turtles and other “herps” do. While hibernating mammals do not drink water, brumating herptiles do.

Cryogenic Chrysalides. The southern journey of the monarch butterfly is well known, but what do other butterfly species do? Many insects, including butterflies like the showy tiger swallowtail (Papilio sp.), build winter contingencies into their life cycles. In fall these butterflies lay their eggs on host plants such as tuliptrees (Liriodendron tulipifera) where the caterpillars will hatch, consume leaves and then enter the pupal stage as they form a chrysalis. These chrysalides can be found on high branches where they are attached by silk throughout the winter and emerge as adult butterflies in spring. By comparison, the mourning cloak butterfly (Nymphalis antiopa) persists in its adult stage in the winter and can be found under tree bark, in mulch animalhibernation_morningcloakpiles or other places that shelter it from wind and predators. Much like the wood frog, this butterfly has blood that has an anti-freeze-like quality. These butterflies are often the first species observed in the spring and will feed on tree sap or animal scat while flowers are still emerging.

Hibernators, Big and Small. The black bear (Ursus americanus) is perhaps the most recognized hibernator, though many biologists would venture to say that these species do not undergo a “true” hibernation. Groundhogs (Marmota monax) are universally recognized as true hibernators, in that their body temperatures drastically drop (from 98 F to as low as 38 F) and their heart rates become very slow (from 80 beats per minute to four or five beats per minute). Unlike groundhogs and other small mammals (such as rodents and bats), bears have a surface-to-volume ratio that allows their heart rate to decline as they hibernate, but not as rapidly and severely as that of the groundhog. Also, their body temperature remains fairly constant throughout their slumber. That said, bears are capable of remaining in their stupor for longer than groundhogs and other rodents. In fact, black bears in northern regions, where periods of mild winter weather are rare, have been known to sleep for seven months straight without waking to eat, drink or defecate. Conversely, animals such as chipmunks store caches of food they can eat when they awake during the winter, then defecate and go back to hibernating.

Animal adaptations to cope with changing seasons help bring additional seasonality to our experiences in the outdoors. While I may spend the winter months longing for days filled with salamanders and box turtles, I do enjoy the winter tradition of juncos returning to my feeder. And, as northern lakes freeze, southern lakes benefit from the arrival of many ducks, swans, geese and other waterfowl that are only found in our region in the winter months.

Adults should be sure to incorporate experiences like winter bird feeding into the daily lives of their children and grandchildren to help cultivate a rhythm to the seasons based on more than animalhibernation_woodlandcovetemperature and layers of clothing. In addition, children can learn more about how our local wildlife cope with the arrival of winter at the Arboretum’s“Storytime at Woodland Cove”, an animatronic wildlife show that features a young bear seeking advice from his “deer” friend Bucky. The story, introduced by a wise old mamma bear, includes dialogue between Bucky and Young Bear as they discuss how they and the other residents of Woodland Cove prepare for and endure winter. Storytime at Woodland Cove is available for viewing as part of the Arboretum’s popular Winter Lights event, which runs nightly now through January 1.