Field Guide to November 2021

Chilly Cocoons

By Julia Pupko

As November begins, we enter stick season, surrounded by the bare, gray twigs of deciduous trees and shrubs. However, the lack of leaves reveals other jewels, if you know where to look for them—giant silk moth cocoons! Giant silk moths (Subfamily Saturniidae) are massive by moth standards, including the well-known Luna Moth (Actias luna). In Vermont, five species in this group have been recorded: Luna Moth, Polyphemus Moth (Antheraea polyphemus), Cecropia Moth (Hyalophora cecropia), Promethea Moth (Callosamia promethea), and Columbia Moth (Hyalophora columbia). These species overwinter as pupa, wrapped snugly in their silken cocoons.

This November, the VAL team is asking you all to join the Cocoon Watch by photographing giant silk moth cocoons and uploading images to the Vermont Giant Silk Moth Cocoon Watch on iNaturalist.

Finding and Identifying Giant Silk Moth Cocoons

Cecropia Cocoons

Cecropia cocoons are longitudinally attached to twigs and branches, or are spun in grasses at the base of a host tree. Cocoons affixed to tree branches are typically tighter and slimmer, while those found in grass are looser and baggier. Their preferred host plants include apple, ash, Box Elder, cherry, lilac, poplar, Sassafras, and willow

It can be useful to search for baggier cocoons at the base of isolated cherry and apple trees growing along fences and roadsides. Cocoons can be found from knee height to about 30 ft. in the canopy. Brush swamps with Black Cherry, Alder, buttonbush, and Glossy Buckthorn may be the most productive natural sites.

Promethea Cocoons

Promethea moth cocoons are spindle-shaped and wrapped into a leaf that remains attached to a bush or tree. The Promethea caterpillar reinforces the leaf with silk to ensure it does not fall from the tree, occasionally encasing the entire leaf.

Cocoons can be found from knee height to about 30 ft. up in the canopy. Searching cherry trees, ash, Sassafras, buttonbush, and spicebush in edge habitats can be very productive.

Luna Moth Cocoons

Luna moths spin their cocoons in leaves on the forest floor. They can be difficult to find. Search near host plants such as Paper Birch, other birch species, Black Gum, hickory, and walnut.

Polyphemus Moth Cocoons

Polyphemus Moth cocoons are also typically found spun in the leaf litter in Vermont. They can also be found longitudinally attached to a twig or hanging from a twig on silk peduncles. Their favorite host plants include birches, trees and plants in the Rosaceae family, and willows.

Columbia Moth Cocoons

Columbia Moth cocoons are typically only found in suitable habitat—boggy areas containing Tamarack (Larix laricina) and other species. Cocoons are brown and spun near the bottom of the trunk of Tamarack or Pin Cherry trees. They may also be found on nearby vegetation.

Make sure you join the Vermont Giant Silk Moth Cocoon Watch project on iNaturalist to receive mission updates. You can learn more about the cocoon watch here.

Hairless Hibernacula

By Julia Pupko

With climate change, winter is coming later. This year, we had a very warm October, with Mount Mansfield breaking its record for the latest freeze date. This means that taxa such as snakes, which do not enter a “true” hibernation during the winter, can still be found out and active on warm days.

Snakes need to find a warm place to stay in the winter. They are cold-blooded, and require a sheltered nook below the frost line. Many snakes of different species will occupy a “hibernaculum,” or a winter den with up to hundreds of individuals, found in deep crevices in rocky areas or old mammal dens. Snakes in a hibernaculum will tightly intertwine themselves to retain heat. Snakes slow their metabolism and stop eating, allowing species that would usually eat each other to cohabitate without incident.

Snakes will sometimes migrate several miles to find a suitable hibernaculum. Some will use the same one year after year, generation after generation. Come spring, keep your eyes peeled when exploring rocky places—on a warm day you may get to see all of the snakes emerging from their winter home.

The Mighty Late Migration

By Abbie Castriotta

Many migratory species, including the Green Darner (Anax junius), Drone Fly (Eristalis tenax), and  Blackpoll Warbler (Setophaga striata), may already be well on their way to their winter homes, but most Red-tailed Hawks (Buteo jamaicensis) are just beginning their southward journey. The mid-point of Red-tailed Hawk migration does not occur until the first week in November, unlike most other raptor species that migrate between September and October. In Vermont, some individuals brave the winter—recent increases in winter counts in northern regions and decreases in fall migration counts indicate that Red-tailed Hawks are responding to climate change by wintering further north and migrating shorter distances during milder winters.

Red-tailed Hawks are the most abundant hawk in North America and one of the most recognizable birds in Vermont. With a four-foot wingspan, Red-tailed Hawks are one of eastern North America’s largest birds in the Buteo genus. Red-tailed Hawks are often first identified by their characteristic brick-red tail, although immature hawks in the East have light tails with brown striping. Key identification features for both adults and juveniles include a light underside with dark patagial (“shoulder” area) marks, a streaked belly, and a dark head. In November, most of the raptors migrating overhead are likely adult Red-tailed Hawks; juveniles often winter further south and migrate earlier in the season to make the comparatively longer journey.

Red-tailed Hawks and other raptors have a few tricks to make their journey south as efficient as possible. Migrating raptors will catch thermals, or updrafts of warm air, and ride them as high as they can before gliding downward to catch the next thermal. These updrafts often occur along mountain ridgelines or above warmer urban areas. Many species of raptors may gather in a thermal, creating an upward spiraling group called a kettle. Higher volume flight days often occur after the passing of a cold front when northwest and west winds produce favorable updrafts on north-south oriented mountain ranges. Raptors will opt to avoid large water crossings during migration and large numbers may be seen passing along flight routes at the edges of waterbodies.

I spent a recent October weekend at a raptor banding station in Cape May, New Jersey, where I was able to observe this phenomenon. Hatch-year raptors have not yet learned about the favorable routes along mountain ranges and many tend to hug the Atlantic coast knowing only that they must avoid the large body of water to their left. As they travel south, they pause at Cape May while investigating the best method for crossing the Delaware Bay. Most decide to travel northwest along the bay and cross the Delaware River, and, if the banders are lucky, with a numbered bracelet around their leg.

You may be able to catch a glimpse of Red-tailed Hawk migration in your own backyard by patiently watching the sky in late morning or early afternoon. For a chance to see large numbers of Red-tailed Hawks passing through, visit your local mountain with a pair of binoculars or one of Vermont’s hawkwatch sites: Mt. Ascutney, Putney Mountain, Killington Mountain, or Mt. Philo where you may get the chance to talk with dedicated community scientists staked out to count passing raptors.

Throughout the winter, keep an eye out for overwintering Red-tailed Hawks and try your hand at identifying individuals to the subspecies level. Of the three subspecies that can be observed in Vermont, the Eastern Red-tailed Hawk (Buteo jamaicensis borealis) is the most common. The Northern Red-tailed Hawk (Buteo jamaicensis abieticola) may be present in non-breeding months but there has been little documentation of this subspecies. Western Red-tailed Hawks (Buteo jamaicensis calurus/alascensis) and Southern Alaskan Red-tailed Hawks (Buteo jamaicensis alascensis) are rarely sighted in the Northeast. Don’t forget to report your sightings to Vermont eBird!

Guts and Ruts

By Julia Pupko

You know the old saying, “You are what you eat”? As we move into winter in Vermont, many species, such as White-tailed Deer (Odocoileus virginianus) take this quite seriously. White-tailed Deer are ruminants, using a four-chambered stomach to process plants and better absorb nutrients. The largest section of a deer’s stomach is called the rumen, where plant material ferments so nutrients can be absorbed better. Deer chew plant material, swallow it, regurgitate and chew it again, then pass it into the rumen for fermentation.

During the winter, food becomes scarce and available food sources change, sometimes drastically. In the summer and fall, White-tailed Deer graze on leaves, grasses, agricultural crops, and fruits. During the winter, White-tailed Deer slow their food consumption, burning fat that they built up from the end of the summer through the fall. Food sources shift to twigs, lichen, fungi, and trees such as Northern White-Cedar. With this change in diet comes a change in gut microbiota, allowing them to digest the woodier material they eat during the winter. A study in Austria found that supplemental feeding shifted the gut microbiota of Roe Deer, which may adversely affect overall health. In fact, feeding deer corn, hay, and other similar material during a harsh winter can actually kill a deer, since their guts become incapable of digesting large amounts of richer foods and they fill themselves up with food they cannot digest.

November is also the peak breeding season for White-tailed Deer in Vermont. Shifts in photoperiod kick off a chain of hormonal changes. After breeding, gestation lasts for around 200 days, or 6.75 months, meaning that young are born between May and June. Breeding timing is very important in northern climates, since early births could lead to fawns freezing to death. Female fawns remain with their mothers for two years, while young males leave their mothers after the first year. This creates multi-generational female familial units that remain together throughout the year. Males typically forage together in small groups, disbanding for the breeding season. During the breeding season (also called the rut), males use their antlers to scrape off strips of tree bark, marking their territory. Males are polyamorous, breeding with multiple females and fighting rival males over a female who is ready to mate. However, males sometimes remain with females for days or weeks after breeding.

Even though White-tailed Deer are pretty common in Vermont, we still encourage you to share any sightings with VAL on iNaturalist!

Barking up the Right Tree

By Abbie Castriotta

I have always enjoyed strolls outside during months—such as November and March—when my attention turns from the stunning seasonal displays of peak foliage, sparkling snow cover, or emerging flowers to the often-overlooked details of the natural world. Tree bark comes into its own in November when the canopy is bare and the low, pre-solstice sunshine highlights the diversity of color and texture. As with everything in nature, these unique adaptations serve a purpose for each species. Many of the variations in bark that we see in our Vermont forests can be attributed to the challenges involved in surviving cold winters.

Unlike plants of the forest floor, such as ferns (Polypodiopsida) and lilies (Lilium), that survive the winter as geophytes (plants with underground water and energy storage organs), or animals that can migrate or seek shelter, trees must weather the winter where they are rooted. Trees face a unique challenge in the colder months: their height exposes them to extreme weather conditions such as ice, wind, and sun. Yes, one of the greatest threats to trees in the winter is the sun. Though the air temperature may be below freezing, the sun can heat tree trunks to temperatures upwards of seventy degrees Fahrenheit, causing the bark and wood to expand. When the sun dips below the horizon or behind the trunk of a neighboring tree, the temperature of the bark can drop dramatically. The outer bark contracts faster than the inner wood, causing a vertical crack. When this happens continually through the winter, the crack will become wider and deeper, weakening the trunk and making it more susceptible to snapping by wind and snow.

Coniferous trees do not rely on their bark for protection—their evergreen branches provide shading to prevent the rapid thawing and refreezing of their trunks. This adaptation allows their range to extend farther north and to higher altitudes than most deciduous trees. The deciduous trees with the furthest north ranges are those with light colored bark: birches (Betula) and aspens (Populus). As you would opt for a white t-shirt on a hot summer day to keep cool, these light-colored trees operate by the same laws of thermodynamics in the winter to reflect sunlight and prevent rapid heating when the sun hits their trunk. Most of our other tree species have furrowed bark such as scales on Black Cherries (Prunus serotina) and Sugar Maples (Acer saccharum) or ridges on White Ashes (Fraxinus americana) and Red Oaks (Quercus rubra). These furrows act as vents to regulate the temperature by releasing heat externally instead of to the interior wood.

As you begin to pay closer attention to tree bark, you may notice some other oddities of texture and color. American Beeches (Fagus grandifolia) have smooth bark to protect against the abundant growth of epiphytes (plants that grow on trees such as mosses and ferns) — a prevalent issue in the tropics where this species evolved. The bark of Balsam Firs (Abies balsamea) appears to be covered in warts, and if you have ever pressed on one with your finger nail, you know that these bubbles are filled with resin—the perfect trap to prevent insects from damaging their canopy and inner wood. Trees such as Red Pine, Shagbark Hickory, and White Oak are adapted to survive in hot, dry sites because their thick, layered bark provides insulation against fire damage and water loss.

For more information about tree adaptations and forest structure, check out Tom Wessel’s book, Reading the Forested Landscape. And don’t forget to share tree bark images to VAL on iNaturalist!