Field Guide to January 2020

Although the days are slowly growing longer, life in the Northeast now finds itself in the coldest depths of winter. January is about survival. Wildlife that doesn’t migrate adapts instead in order to make it to spring. Here’s a few tidbits of natural history happening outdoors this month around you.

Winter Lodging

By Emily Anderson

When life gives you flowing water, you dam it. At least, that’s the motto of beavers. These furry engineers are a common sight on many of Vermont’s streams, marshes, ponds, and lakes, however they vanish when winter sets in. But, they don’t hibernate. When the weather turns cold, beavers remain indoors, living out the winter on edible tree branches stored underwater near their lodge. It takes about one ton of bark to last a family of eight beavers through the winter. This means that they spend the fall busy as, well, beavers in order to amass enough wood to last them until spring arrives.

Underwater is not the only place that beavers store sustenance. Much like other animals that overwinter in the north, beavers put on a layer of body fat to stay warm, as well as to provide insurance against food shortages. In particular, a beaver’s tail is designed to store fat and will shrink as its supplies are depleted. In cases of emergency food shortages, beavers will venture onto land, however their ambling gait and winter snow make them easy prey for predators like coyotes.

Besides food, warmth is the other factor crucial to a beaver’s survival in winter. Luckily, beavers’ thick, waterproof fur provides excellent insulation against both cold temperatures and freezing water. Beaver lodges also trap heat fairly well, keeping the interior above freezing even when the outdoor temperatures are below zero. The more individuals who can contribute body heat, the warmer the lodge remains. And sometimes, the beaver family is not alone in the lodge. Occasionally, muskrats and mice will join the beavers, sharing the warmth and safety provided by the lodge.

For more information on beavers in winter, listen to this episode of Outdoor Radio. If you want to learn more about beaver’s life cycle and history in Vermont, then check out their VT Fish & Wildlife Department webpage.

A Bark in the Night

By Kent McFarland

Adult Red Foxes are usually solitary until mating season, which begins this month and lasts until early March in New England. Red Fox attract each other with series of barking at night. High-pitched screams or barks at night, often thought to be Fisher, are usually calls from fox. Fisher are quiet animals.

Listen to the distant barking screams of a Red Fox recorded in Woodstock, Vermont.

During the cold New England winters, red foxes stay warm by growing a long winter coat. An adult fox rarely retreats to a den during the winter, but will instead curl into a ball in the open, using its bushy tail to wrap around its nose and footpads. Many times, they can be found completely blanketed in snow. With the onset of spring, red foxes shed their winter fur and prepare for warmer weather.

It Takes Guts to Survive a Boreal Winter

By Kent McFarland

Spruce Grouse eat low fiber foods in summer, mostly fruit and insects. But in winter, they switch to a diet of very high fiber when they eat mostly conifer needles. They forage at mid-crown level, perhaps because these needles are more palatable or higher quality; the branches are larger and also provide sturdy support; and they can see approaching predators while remaining better concealed in thicker foliage.

Back in the 1960s, biologists B. A. Pendergast and D. A. Boag wondered if this seasonal change in diet was accompanied by structural changes in the Spruce Grouse digestive system. For an entire year they sampled grouse each month in Alberta, Canada to find out. In their 1973 paper, they reported that Spruce Grouse gastrointestinal organs did change with seasonal shifts in diet.

In winter, when the birds ate more and poorer quality food to maintain their mass and energy balance, the gizzard grew by about 75%, and other sections of the digestive tract increased in length by about 40%. Captive birds from the same population that were maintained mostly on poultry feed did not have the same size or degree of seasonal gastrointestinal tract change. It takes guts to survive the long, dark winters in the boreal forest.

Peeling Bark

By Kent McFarland

While snowshoeing in the high elevations of the Green Mountains of Vermont recently, I was struck by how many large White Birch (Betula papyrifera) trees there were. All of them had the tell tale peeling paper-like bark. Some of them with long strips flapping in the cold wind. And then it struck me, why does birch bark peel?

On my hike back I came up with a couple of ideas. Maybe as the tree grows the weak bark splits and peels away exposing a new skin underneath. Sort of like a snake that sheds its skin as it grows. The bark is white for a reason I suspected, so maybe they peel to just stay clean. But why do they need to be white and clean?

It turns out that this unique characteristic may allow birch trees to shed lichen and moss that grow on their trunks over time. The epiphytic curtain covering the trunk darkens them causing problems for the tree in both winter and spring.

In the early spring birch bark can photosynthesize, giving the trees a head start before any leaves are fully opened. This is a great advantage for a pioneer species like White Birch as it can outcompete other trees because it can grow before others have leaves closing the canopy.

The biggest advantage may be during the winter. Darkened trunks can be disastrous for birch trees. The sun is low on the horizon during the winter and the sun’s rays strike more directly on the trunk. White bark reflects the sun on bright cold days. Even in the dead of winter the sun is quite strong. Stand with a pair of black ski pants facing the sun and even when it is brutally cold you can feel the sun heat up your legs as the black fabric absorbs the sun’s energy. But, when a birch trunk is exposed to heating of the sun on very cold days it can lead to frost cracking as it expands and contracts quickly. Cracks in the trunk can heal with scar tissue, but more often it leads to the trees slow demise as rot and disease attacks the wood. Shedding bark keeps the tree clean and healthy.

Snowbird Social Life at Your Feeder

By Kent McFarland

Dark-eyed Juncos, also known as ‘snowbirds’, spend the winter in small flocks. Each flock has a dominance hierarchy with adult males at the top, followed by juvenile males, and females at the bottom. Watch them at your feeders and you can often observe individuals challenging the status of others with aggressive displays of lunges and tail flicking. But the farther north you are, the fewer females you will see in the flock.

To avoid competition, many females migrate farther south than most of the males. Up to 70% of Juncos wintering in the southern U.S. are females. Males tend to stay farther north in order to shorten their spring migration and perhaps gain the advantage of arriving first at prime breeding territories.

Ruffed Grouse Warm Under a Blanket of Snow

By Kent McFarland

Where’s the warmest place for a bird to spend the night? Depending on the temperature, it might be subnivean. WIth the air temperature dropping well below freezing, a deep blanket of snow might be the insulation that separates life from freezing death for a Ruffed Grouse. You can find places they’ve roosted by the marks in the snow showing where they entered and where they exited their winter den. They may even burst out of the snow in front of you, frightening you into a warmer state. On a warmer night or when snow conditions are poor, grouse may settle for roosting in the branches of an evergreen tree.

Each fall Ruffed Grouse grow comb-like rows of bristles (called pectinations) on their feet. These create a “snowshoe” effect for the grouse, allowing them to walk on the surface of the snow. Grouse also have extra feathers that cover the nostrils on the beak to make the air just slightly warmer as it enters their airways, like a balaclava mask you might wear on a cold winter day.