Wildlife Sanctuary Almanac: Where Do They Go?

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.

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Catch up on past Wildlife Sanctuary Almanac articles here.

Wildlife Sanctuary Almanac: Grow your own bird feeder for migrating birds

Photo: Blackpoll Warbler, Kevin Sim/Audubon Photography Awards

Betsy Martin

Hurricanes Helene and Milton posed special challenges during this fall’s migration. Migration ecologist Andrew Farnsworth of the Cornell Lab of Ornithology estimated that 150 to 275 species were in the midst of migration during the hurricanes, which interrupted the migration of more than 100 million birds crossing over Alabama, according to the Washington Post.

Even without hurricanes, migration poses challenges that defy imagination. Take, for example, the Blackpoll Warbler (Setophaga striata). The Blackpoll Warbler does not breed in northern Virginia, and only shows up here while migrating to and from its breeding grounds in conifer forests far north in Alaska and Canada and its wintering grounds in South America.

This small bird weighs less than half an ounce, about as much as two quarters. Yet, it undertakes the longest migration of any North American warbler. Some individuals travel almost 5,000 miles from Alaska to Brazil. In fall, they travel south and southeast through Canada and the northeast U.S., and collect along the coastal plain between Nova Scotia and Cape Hatteras, NC. Then, it’s believed (the experts aren’t really sure), they head south and southeast over the Atlantic, and fly nearly 2,000 miles to Puerto Rico, the Lesser Antilles, or northern South America. This may involve an 88-hour nonstop flight over the open ocean! They ride northeast trade winds to direct their flight toward South America.

Sassafras drupes are a favorite of early fall migrants, such as Eastern kingbirds. The red pedicels signal the fruit is ripe. Photo: Betsy Washington

To accomplish this amazing feat, Blackpoll Warblers nearly double their weight before setting out. They add fatty fruits to their diet of bugs and caterpillars. They eat any late summer or fall fruits, but it’s the native ones that have the high fat content they need to sustain them on their long journey. 

Blackhaw. Photo: Courtesy of Dyck Arboretum of the Plains

Migrating birds make periodic stopovers to eat and replenish their energy reserves. Make your yard a wildlife sanctuary for them by planting native fruiting shrubs, trees, and vines. Good choices for migrants that also make nice landscape plants in northern Virginia include Arrowwood, Blackhaw, or Possomhaw viburnums (Viburnum dentatum, V. prunifolium, V. nudum), Virginia creeper (Parthenocissus quinquefolia), Silky, Gray, or Flowering Dogwood (Swida amomum, S. racemosum, Benthmidia florida), Spicebush (Lindera benzoin), American beautyberry (Callicarpa americana), and Sassafras (Sassafras albidum). Bayberry’s (Myrica cerifera) wax-coated fruits can only be digested by a few migrant species (Yellow-rumped warbler and Tree swallow) so this plant is not useful to most migrants. Fruits of other native fruiting trees, such as American holly (Ilex opaca) and Hackberry (Celtis occidentalis) ripen too late to be useful to fall migrants, but are good food sources for wintering species. All of these shrubs and trees set more fruit if planted where they get sun. You can find out more about their characteristics, requirements, and eventual size here. 

Fall-fruiting native shrubs and trees not only provide nutritious, fatty berries for birds, but also display beautiful fall color. That’s not for our benefit: what’s called foliar fruit flagging is the way the plants signal to birds that fruits are ripe and ready for plucking—just in time for migration.

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Catch up on past Wildlife Sanctuary Almanac articles here.