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Winter sunset Kent McFarland

Field Guide to December 2023

Fear not—during December's short days and long nights, there’s still plenty of life in the fading light. Once we pass the winter solstice, which strikes at 10:27 PM on December 21, more light will creep back. Until then, here’s some wintry natural history to keep you going.

By Vermont Center for Ecostudies December 7, 2023
Male and female Evening Grosbeaks © tuchodi, CC by 2.0
Male and female Evening Grosbeaks © tuchodi, CC by 2.0

Evening Grosbeaks: A Winter Visitor in Steep Decline

By Desiree Narango

In the deep throes of a New England winter, you may get lucky to have a flash of golden yellow from an Evening Grosbeak (Coccothraustes vespertinus) brighten your day. Evening Grosbeaks are large finches (just a bit bigger and bulkier than a cardinal) found year-round in Vermont, but they are most abundant here in winter. December is when breeding individuals from the boreal forests of northeastern Canada make their way southward to spend the winter in our region. Male Evening Grosbeaks are identified by their striking yellow and black plumage, heavy pale bills, prominent white patch in the wings, and yellow ‘eyebrows.’ Females and immature birds are more gray and pale greenish-yellow but also have heavy pale bills and bold white on their wings.

Although almost exclusively insect-eaters during the summer, they are particularly fond of visiting bird feeders in the winter and can often descend in large flocks to feast on your seeds. Last winter, when I first moved to Vermont, I was thrilled to have a flock of nearly 50 birds visit daily, filling my trees with cheerful chips and chirps. They are considered ‘irruptive’ migrants, with some years having unusually high numbers of individuals moving southward due in part to food shortages in more northern parts of their winter range.

The large numbers I saw at my feeder belie their mysterious recent declines. According to Partners in Flight, Evening Grosbeaks have experienced the steepest declines of any other North American land bird, declining more than 92% in the East since 1970. Project Feeder Watch community scientists have documented a 50% reduction in feeder visits and a 27% decrease in average flock size in only two decades. The causes for their decline are unknown but are likely due to one or more anthropogenic factors such as habitat loss, pesticides, window collisions, and climate change. In addition to their alarming declines, scientists have realized something else about Evening Grosbeaks: we lack basic information about their habitat use, diet, and migratory patterns. Understanding the basic ecology of this species is an essential first step toward developing management approaches to help conserve this species.

The Evening Grosbeak Working Group has started to gather this basic information to help save this species. Participants in this working group have noted a significant lack of knowledge about New England birds, which we plan to start filling in this winter. If you see any Evening Grosbeaks, we hope you will share your observations with VCE to help us identify locations and flock sizes around Vermont and New Hampshire. These data will help us identify areas for field work this winter, when we will capture birds to attach transmitters to track migration and quantify survival. You can report your sightings in Vermont eBird or post your photos or sound recordings on iNaturalist. Our scientists may even contact you to collect follow-up data on your birds if you are interested!

Panorama of a fir wave © Kent McFarland
Panorama of a fir wave © Kent McFarland

Ice, Snow and Wind Move Fir Waves Across the Mountains

By Kent McFarland

Economically and ecologically important, Balsam Fir is a keystone species of the eastern North American boreal zone. This provincial tree of New Brunswick, Canada, can form dense single species stands in some areas of northeastern North America, especially in the high mountains.

High-elevation forests are often marked by “fir waves,” crescent-shaped bands of dead trees that you can see in systematic patterns across mountainsides. The waves are areas of standing dead fir trees with healthy trees surrounding them. Trees at the leeward edge of the canopy opening in the wave die from loss of needles and branches due to heavy ice accumulation. Being rocked by the wind while supporting ice loads also causes their fine rootlets—important for delivering nutrients to the tree—to break underground. As these trees die, adjacent trees experience the same conditions and begin to die. 

Fir waves move very slowly, over decades, in the direction of the prevailing wind. Wind velocity at the edge of the tree canopy is over 50% higher than within the forest. Regeneration of waves occurs at about 60-year intervals. As you move back from the dying front of trees, the trees become increasingly older until you reach the following wave of dead trees. If you were to take time-lapse photography, the waves of dead trees would appear to be moving across the mountainside like a wave in the ocean.

Deer Mouse/White-footed Mouse (genus <i>Peromyscus</i>) © Sarah Carline
Deer Mouse/White-footed Mouse (genus Peromyscus) © Sarah Carline

Mice on Ice

By Julia Pupko

In Vermont, we have two native mouse species (White-footed Mouse (Peromyscus leucopus) and Deer Mouse (Peromyscus maniculatus)) and two native jumping mouse species (Meadow Jumping Mouse (Zapus hudsonius) and Woodland Jumping Mouse (Napaeozapus insignis)). Of these species, only the Meadow Jumping Mouse and Woodland Jumping Mouse hibernate. But what about Vermont’s two other mouse species? 

White-footed Mice are found across much of the United States and possess different regional adaptations to their local climates. For example, the peak breeding season of southern White-footed Mouse populations occurs in winter, when temperatures are cooler. However, for northern White-footed Mouse populations, surviving harsh winters demands immense energy expenditure, making breeding in warmer months more advantageous. 

Despite freezing temperatures, White-footed Mice remain active throughout the winter, occasionally entering torpor for short periods on exceptionally cold days. They sometimes cache food and nest communally with other White-footed Mice for warmth. In northern climates, White-footed Mice make thicker, more insulated nests to reduce the amount of energy needed to stay warm while in their nests. Generally, White-footed Mice are highly adaptable and readily change their behavior in response to environmental conditions.

Deer Mice implement many adaptive measures comparable to White-footed Mice in winter. Deer Mice create nests both above and belowground, utilizing abandoned burrows for underground nests. They also nest in groups during the winter for warmth, sometimes in groups greater than 15 individuals. Deer Mice are aggressive winter food cachers, with one individual caching up to 3.2 quarts of food for the winter in hollow logs and other protected areas.  As with White-footed Mice, the timing of Deer Mouse breeding season depends on the local climate. In Vermont, Deer Mice typically stop breeding before December.

These two species sometimes nest together during the winter and leave tail-drag marks when they travel on the snow’s surface. As the December snow starts to fall, keep your eyes open for tiny tracks in the snow with the tell-“tail” imprint. And make sure to share them with the Vermont Atlas of Life on iNaturalist!

Dark Fishing Spider <i>(Dolomedes tenebrosus)</i> © Kent McFarland
Dark Fishing Spider (Dolomedes tenebrosus) © Kent McFarland

Spiders in Winter

By Susan Hindinger

Winter can be tough on all of us. It’s cold, our lips get chapped, and fresh veggies are hard to come by. It turns out spiders have their own versions of these very challenges to manage. When winter’s cold sets in, spiders employ strategies that many other organisms use to deal with the cold, dry air, and lack of food—either they go dormant, remain active, or lay eggs and then die.

Spiders are “poikilothermic,” meaning their body temperatures vary significantly, more or less tracking that of their environment. The chief challenge of winter for spiders in the temperate zone, then, is dealing with the cold.

As many as 85% of the temperate spider species go dormant for the winter, hunkering below the leaf litter. Their metabolism slows, their legs draw up tight against their bodies to conserve heat and moisture, and they wait it out. They can go months without a meal, although they are not truly hibernating and will dine if the opportunity presents itself. Where a blanket of snow insulates the ground, spiders maintain body temperatures around 0 degrees Celsius even when the temperature above the snow is much colder by exploiting a comparatively warm microhabitat much as subnivean rodents do. This environment also retains more available moisture than unprotected places, so dormant spiders successfully avoid desiccation.

Some spiders—including some of the smallest members of the family Linyphiidae (1–5 mm in size)—actually remain active in the winter. With elevated metabolic rates, this group is at risk of not only freezing but starving as well. Feeding upon winter-active Collembola (the springtails you see on the snow’s surface as if someone spilled their pepper shaker) and any other prey they can find, these spiders can remain active until their body temperature reaches -4 degrees Celsius when they will go dormant like other spiders. If they cool to -7 degrees Celsius, they die.

Exactly how spiders achieve their cold-hardiness remains a mystery. Glycerol, the same “antifreeze” compound that prevents the blood cells of some amphibians from freezing in winter, is found at elevated levels in the hemolymph (the spidery version of blood) during winter. And while this can explain a modest lowering of the freezing temperature for spiders, it only accounts for a one-degree decrease. Some garden spiders can withstand temperatures as low as -20 degrees Celsius, even in unprotected places, and scientists simply do not know how.

Aside from seeking protected microhabitats (like leaf litter), spiders adopt behaviors that proactively control body temperature. They bask. As the weather cools, a spider builds its web oriented east-west so that its body receives the full impact of the sun’s rays while on the web. (Who among us has not found a protected south-facing spot to soak up some rays on a cold winter day?) In hot environments, it will do just the opposite, orienting its web sideways to the sun. Some studies even suggest that female spiders build webs to control body temperature as temperatures drop, thereby extending their reproductive season. Spiders minding their egg masses have been shown to take them underground to moderate their temperature, and to bring them back out into the sun to warm them up. And somehow—mysteriously—through these behaviors, spiders can maintain their body temperatures several degrees above or below the ambient temperature of their environment. They manage it, though, without the benefit of polar fleece or goose down—yet another reason to marvel at these diminutive, creative engineers.

Wood Frog newly emerged in spring from a long winter nap. © Kent McFarland
Wood Frog newly emerged in spring from a long winter nap. © Kent McFarland


By Kent McFarland

By now, most frogs are frozen. But in a few months, they’ll croak up a storm in the pond, back from the frozen, the nearly dead. How do they do it?

In late autumn, ice begins to form inside Wood Frogs’ bodies. Glucose levels increase in their blood by as much as 200-fold in just eight hours, creating an antifreeze that preserves their tissues through the long winter. The ice penetrates throughout their abdominal cavity, encasing all the internal organs. Large, flat ice crystals form between the layers of skin and muscle, and frozen lenses make their eyes white like zombies. Their blood stops flowing. As much as 65% of the frog’s total body water is locked in ice. Breathing, heartbeat, and muscle movements all stop. The frozen frogs, or frog-sicles, are in a virtual state of suspended animation until spring.

A young moose photographed by Ed Sharron in Rochester, VT. © Ed Sharron
A young moose photographed by Ed Sharron in Rochester, VT. © Ed Sharron

Warmer Winters Mean Trouble for Moose

By Emily Anderson

The Moose, northern New England’s unofficial mascot, haunts the imagination of hunters, photographers, and wildlife enthusiasts alike. In warmer months, these graceful woodland giants forage in areas where nutrient-rich aquatic plants are abundant, sometimes diving 18 ft deep to reach their food. In the frigid months when aquatic vegetation vanishes, moose, too, must disappear from their watery feeding grounds to pursue woody plant material, such as twigs and bark. These food sources offer distinctly fewer calories than their summer feed, making energy precious and its conservation vitally important.

However, moose are designed for harsh winters. Although often seen as similar to deer, moose cope more easily with deep snow thanks to special joints that allow them to lift their hooves straight up nearly to shoulder height. Even in feet of snow, moose can move with relative ease and expend less energy when traveling or escaping predators. However, unlike deer, moose are at significant risk of overheating in the summer due to their large size and thick fur, which help them weather bitterly cold northern winters. As the climate warms, these traits, which make them perfectly suited to the icy north, will become a greater disadvantage, possibly affecting their survival.

Moose are also facing another significant threat to survival: winter ticks. New England winters are becoming warmer and shorter due to climate change. In the past, freezing temperatures and heavy snows have caused tick populations to decline right when they are searching for a host. In contrast, milder winters fail to dent their populations, meaning moose can accumulate higher numbers of tick nymphs. Unlike deer, moose do not regularly engage in habitual grooming. Ticks often go through several life stages on a moose and reach their final, most voracious state before the moose notices its passengers and tries scratching them off. By that time, it is usually too late. Studies have found tick counts ranging from 10 to 100,000 individuals per moose. These large infestations lead to increased calf mortality and decreased female breeding success.

The likelihood of milder winters coupled with the reduction in reproduction and calf survival means that New England moose face an uncertain future. For now, biologists are monitoring their populations and working with other state officials to develop the best management path forward.

If you want to learn more about moose and ticks, visit the VT Fish & Wildlife Department or check out this episode of Outdoor Radio. If you see moose sign when exploring backcountry trails this winter, make sure to share your observations with the Vermont Atlas of Life on iNaturalist.

Dwarf Mistletoe on Black Spruce. © Bryan Pfeiffer
Dwarf Mistletoe on Black Spruce. © Bryan Pfeiffer

A ‘Little’ Kiss Beneath the Mistletoe

By Kent McFarland

Mistletoe has been a symbolic plant for thousands of years. In Europe, it became associated with Christmas as a decoration under which lovers were expected to kiss, a tradition that continues in many places today. Of course, this was the European Mistletoe (Viscum album), the only native mistletoe species that ranges across most of Europe. The tradition was carried to the New World, where American Mistletoe (Phoradendron leucarpum) was adopted for this purpose. But if you live here in the Northeast, you won’t be able to harvest your own mistletoe to hang for the holidays; American Mistletoe only grows in the southern portion of the continent. However, we do have a unique mistletoe lurking in our forests—but it looks nothing like the others.

Like other mistletoes, Dwarf Mistletoe (Arceuthobium pusillum) is a bit of a thief, actually a hemiparasite, which means it steals minerals and fluids from its host plant and also generates some of its own energy through photosynthesis. It grows within the branches of pine, spruce, fir, and larch, sometimes causing unusual growths of twigs on the host, called witches brooms.

After a couple to perhaps a dozen years of growth inside the host plant, Dwarf Mistletoe sends reddish-colored aerial stems out of the host branch that bear flowers and fruit. The fruits ripen and fill with fluid, building up pressure until they explode. The sticky seeds can be launched up to 20 feet. And, if they stick to a suitable host branch, they germinate. Of course, the seeds may spread much longer distances by animals, too. The new plant penetrates past the cambium layer and into the host’s xylem and phloem tissues, where it steals the nutrients needed for its own growth and reproduction.

Dwarf Mistletoe isn’t an easy plant to find. It’s rare in the Northeast and listed as endangered in Connecticut, New Jersey, and Rhode Island, as well as threatened in Pennsylvania. We’ve found it on evergreen trees in a few bogs here in Vermont. So keep your eyes open for the aerial stems on host plants, and if you find one, please do kiss and tell! Snap a photo (of the plant!) and report your sighting to the Vermont Atlas of Life on iNaturalist!

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