Photo: Wood Frog, VA Herpetological Society
Betsy Martin
Where do animals go in the winter, when many seem to just disappear?
The ancients puzzled over the disappearance and reappearance of birds. Aristotle thought they transformed into other species in winter, which explained why robins appeared just as redstarts disappeared in Greece. In the 16th century, Olaus Magnus theorized that swallows buried themselves in clay at the bottom of rivers in wintertime. In the 17th century, Charles Morton offered the most fantastic theory of all, that birds flew to the moon and back every year.
We know now that migration on earth accounts for the disappearance and reappearance of birds. But what about other creatures? Learning their whereabouts give us the chance to help many of them overwinter and reappear in the spring.
Butterflies and other insects
We know that some butterfly species migrate, just like the birds, although often we do not know their destination. We can see thousands of Cloudless Sulphurs, Mourning Cloaks and Monarchs move south, but we don’t always know exactly where they go. Most Monarchs from west of the Rocky Mountains winter along the California coast, while those from central North America winter in roosts in the mountains of central Mexico. Some Monarchs from the Atlantic seaboard may migrate to the same Mexican overwintering sites, but others may travel to Florida, possibly joining up with resident, non-migratory populations. Or they may migrate beyond to undiscovered sites in the Caribbean or the Yucatan Peninsula.
Still other summer butterflies do not survive the winter. But each year, as the weather warms, butterflies from Mexico and the southern United States fly north to repopulate Virginia. Examples include Common Buckeye, Cloudless Sulphur, Painted Lady, and Red Admiral.
But many insects don’t leave at all--they shelter in micro-habitats under the soil, inside rotting logs, in tree holes, inside plant galls, in leaf litter, or under rocks. Insects can enter a dormant state, called diapause, with a metabolic rate barely high enough to keep them alive. Some larvae replace the water in their bodies with glycerol, a type of antifreeze. Still other insects lay eggs that survive winter.
Wood Frog, VA Herpetological Society
Frogs and toads
We know that frogs and toads hibernate. After finding or making a living space (hibernaculum) that protects it from winter weather and predators, its metabolism slows and it "sleeps away" the winter, then "wakes up" when spring arrives.
Terrestrial toads such as American Toads (Bufo americanus) and other good diggers burrow deep into soil to hibernate below the frost line. Wood Frogs (Rana sylvatica), Spring Peepers (Hyla crucifer) and other less-adept diggers seek out deep cracks and crevices in logs or rocks, or just dig down as far as they can in the leaf litter. Their living spaces or hibernacula are not well protected from frigid weather and may freeze, along with their inhabitants.
And yet, the frogs do not die. A high concentration of glucose in the frog's vital organs prevents freezing, even though ice crystals form in its body. A partially frozen frog stops breathing, its heart stops beating and it appears dead. But when the hibernaculum warms up, the frog's frozen portions thaw, its heart and lungs resume activity and it comes back to life.
Various species have amazing and diverse strategies for surviving winter. You can help them thrive by gardening with awareness of their seasonal needs.
To help the creatures that remain survive the winter:
Wooly Bear Caterpillar, Sheila Sund from Salem, United States, CC BY 2.0 , via Wikimedia Commons
Leave the leaves. Leaf litter is key to many species’ winter survival, both insects and foraging birds that live here year-round.
Don’t be too tidy about cutting and cleaning up dead flower stems and stalks. Many insect pupae attach themselves to dead stalks, and adults lay eggs or burrow into stems for winter protection. Don’t throw away next spring’s crop of butterflies and insects by chopping up all the dead stems.
Leave woody debris. Some animals find or create their winter homes in woody debris like logs and large branches.
Be careful about digging or raking in winter. You may be digging up somebody’s winter home. If you do accidentally uncover or dig up an apparently lifeless frog or woolly bear, or firefly larvae, gently cover it up again and leave it to its winter sleep.
Winter is a good time for any tree work or removal you need to do. Doing such work in spring or summer risks destroying bird nests and nestlings.
To help migrating birds:
Plant fall-fruiting native shrubs to help migratory birds survive their fall migration south.
Avoid using insecticides that kill the insects that birds depend on to feed their young when they return to breed in the spring.
Learn more about creating your own Wildlife Sanctuary here. You can request a visit by a Wildlife Sanctuary Ambassador who will advise on habitat improvements you can make on your property. Winter is our slow season, and a good time for a visit to start planning for spring.
Catch up on past Wildlife Sanctuary Almanac articles here.