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Virginia Opossum Tracks

Virginia Opossums have extended their range far enough north that even in parts of northern New England they are present and remain active year-round.  Opossum tracks in the snow provide an opportunity to observe the unusual toe structure of these marsupials. 

Opossums have five toes on all four feet.  The toes on their front feet can spread wide apart, often resulting in a star-shaped track.  The inside toe of their hind foot, or “thumb,” is opposable, has no nail, and often points in the opposite direction of the other four toes. (Thanks to Connie Day for opossum track photo op.)

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North American River Otters Use Abandoned Beaver Lodges As Dens

North American River Otters use dens (called holts) for giving birth and for shelter from weather extremes.  Den sites are usually close to the water line of rivers and lakes, and have multiple entrances underwater as well as on dry land.  They are often excavated under trees or rocks or in river banks, but otters also use abandoned muskrat burrows and beaver lodges as shelters (cohabitation with beavers has also been documented – see https://naturallycuriouswithmaryholland.wordpress.com/2013/02/22/beaver-otter-cohabitation/).

One of the most obvious and distinctive signs of otter occupancy of a den is the presence of their scat in the vicinity.  It usually has little form; rather, it consists of loose piles primarily composed of fish scales. Pictured is an abandoned beaver lodge that is currently occupied by several otters whose scat in the foreground and tracks and slides in the vicinity confirm their presence. A lack of any beaver sign indicates the lodge has been abandoned by its original inhabitants.

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American Tree Sparrows : Winter Visitors

One of New England’s common winter visitors from the far northern tundra is the American Tree Sparrow (Spizelloides arborea), often spotted in large flocks in weedy, snow-covered fields moving from one spot to another as they feed..  These seed-eating sparrows are known to beat weeds with their wings and then fly to the surface of the snow beneath the weeds to retrieve seeds they have caused to fall.  

Their common name is a misnomer, for American Tree Sparrows feed on the ground and often breed and nest on the ground above the treeline.  They apparently reminded European settlers of the Eurasian Tree Sparrow (Passer montanus), a cavity-nesting bird which has very different habits than the American Tree Sparrow. 

In part because of the loss of weedy old fields and other open habitats, the American Tree Sparrow population has declined by 53% over the last 50 years.  Even so, they are a common sight during the winter in fields, on road sides and at feeders throughout the northern half of the United States.

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Bobcats Preying On Rabbits & Hares

Bobcats are capable of preying on animals as large as White-tailed Deer (which they rarely do), but far more frequently they choose the easier-to-catch rabbit or hare. Typically at dawn or dusk a Bobcat will head out to locate and stalk its prey, slowly getting close enough to pounce on it.  Although they sometimes eat their prey immediately, Bobcats often carry it to a concealed area under brush where they eat it. (see photo).  In this scene, in addition to leaving some of the hair of the Eastern Cottontail Rabbit it consumed, the Bobcat defecated, leaving its blunt-ended, segmented scat as further evidence of its presence (lower right in photo). (Thanks to Jody Crosby for photo op.)

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White-winged Crossbills Foraging

Most of New England is privileged to see White-winged Crossbills (Loxia leucoptera) only during the winter, when these nomadic birds forage south of their far northern boreal forest breeding grounds for conifer seeds during poor cone crop years. 

Spruce seeds are the preferred food of White-winged Crossbills. Their crossed mandibles allow them to pry open cone scales and they then extract the seeds with their tongue.  Individuals can eat up to 3,000 conifer seeds a day!

These birds have been documented nesting every month of the year.  As long as they can find a source of food that is sufficient for egg formation and that is likely to remain for the next month or so when they’ll be feeding nestlings, they will breed.  The larger the spruce cone crop, the longer a span of time crossbills typically nest.  Nesting usually declines by November although young do occasionally fledge in December and January. (Photos of a male White-winged Crossbill by Erin Donahue.)

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Gray Squirrels Mating & Making Nests

Gray Squirrels have two breeding seasons, one from December – March and another May – July (most females mate in the latter season and only mate once a year).  At this time of year, polygamous male Gray Squirrels are aggressively chasing and checking out females to see if they are in estrus and if they are receptive. (An unreceptive female squirrel lets all suitors know in no uncertain terms – using claws and teeth – that she is not interested.)  Male Gray Squirrels can smell females in estrus as far as half a mile away, so the woods are full of hopeful males these days.

Frequently litters this time of year are born in a tree cavity, while the second, late-summer litter is born in a leaf nest (drey).  Cavities obviously offer more protection from the elements and predators than do leaf nests. Most den cavities have been created by decay, lightning, or woodpeckers and are lined with dry leaves, shredded bark and grasses. (Photo:  Gray Squirrel collecting American Beech leaves to be used as a lining for her cavity nest.)

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Spiders On Snow

The internal body temperature of spiders is variable and tends to fluctuate with their environment.  This means that the cold temperatures of winter pose a challenge. Spiders meet this challenge in one of several ways.  A majority (as many as 85%) of species crawl under the leaf litter, shut their metabolism way down and become dormant; some species mate, lay eggs and die; and some remain active. 

It is not unusual to come across tiny active spiders on top of the snow, especially on sunny winter days. If it’s particularly cold, they may have their legs pulled in and appear lifeless.  When their body is sufficiently warmed up, they will resume crawling across the snow. 

The metabolism rate of spiders that remain active through the winter is elevated, making starvation as big a threat as freezing.  They must find food (springtails and other invertebrates) in order to sustain themselves.  Some of these spiders can remain active until their body temperature is 25 F degrees when they will go dormant like other spiders. They cannot survive If their internal temperature drops to 19 F. degrees. (Source, Vermont Center for Ecostudies) (Photo: active spider surviving despite loss of one leg)

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Meadow Vole Circles

Congratulations to “Maine Naturalist” and Stein for identifying not only that a Meadow Vole made the mystery tracks, but why they were circular! Thank you all for your comments, many of which were laughter-producing!    

More NC readers have witnessed this phenomenon than I would have imagined – the tracks were made by a Meadow Vole that had neurological problems which could have been caused by a brain parasite, brain tumor, inner ear infection, or a stroke. While the exact nature of an affected vole’s neurological impairment cannot be confirmed without the vole in hand, it is highly likely that a common brain parasite, Toxoplasma gondii, is responsible for a vole running in circles.

The snow-covered corn field where these tracks were located was just down the road from a dairy farm, where it’s likely cats could be found. This is relevant because cats pass this particular parasite on to rodents (and birds) who eat the cats’ feces.  The parasite goes to work on the brains of animals that have eaten cat feces, causing them to become disoriented (to the point where they lose their fear of cats).  Cats then eat the fearless rodents and the cycle continues.  When infected and disoriented, the rodents will often run in circles – hence, the unusual track pattern in the snow.

 T. gondii can infect humans, too, through consumption of under-cooked foods, contaminated drinking water, and through contact with cat feces.  This is why pregnant women are discouraged from tending kitty litter boxes, as the parasite can infect their unborn children.

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Mystery Photo Hint

The circles are roughly a foot in diameter, the tracks approximately 1/2″.


Mystery Photo

What or who do you think is responsible for these tracks in a snow-covered corn field?  To respond, go to the Naturally Curious blog (www.naturallycuriouswithmaryholland.wordpress.com ), scroll down to “Comments” and enter your solution to this mystery!  Answer will be announced this coming Friday, 2/5/21.

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Downy Woodpeckers Foraging For Overwintering Insects

Three-quarters of a Downy Woodpecker’s diet consists of animal matter, mostly beetles, weevils, ants, wasps, bees, true bugs, caterpillars, spiders and snails.  The pictured male Downy has located and is consuming some overwintering wood boring beetles.  

 Notice he is on a small branch.  Research shows that male Downys tend to forage on small-diameter branches and stems of weeds, whereas females are often found on larger branches and the trunks of tree.  

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Blue Eastern Cottontail Urine

A recent (1/22/21) Naturally Curious post on the color of Eastern and New England Cottontail and Snowshoe Hare urine mentioned that occasionally it turns blue after a few minutes in the sun due to consumption of the twigs and bark of the invasive shrub, European Buckthorn (Rhamnus cathartica). At the time of the post I had not had the opportunity to photograph it, but recently came across some so thought I would share it with you today!

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Eastern Gray And American Red Squirrel Food Caching Strategies

Red and Gray Squirrels both store food for the winter, but their food caching strategies are very different. Gray Squirrels store many hickory, oak and beech nuts by engaging in “scatterhoarding” – burying one nut at a time, each in a different spot.  Most popular are acorns, which fall into two groups — those grown by white oak species , and those from the group of red oaks. The acorns of red oaks have delayed germination, making them ideal for storage through the winter.  Those of white oaks germinate sooner, in the fall, so are more readily eaten than buried.  (If a Gray Squirrel chooses to bury an acorn from one of the white oaks, it often removes the embryo before doing so, which kills the seed and prevents germination.)  

Red Squirrels, on the other hand, practice “larderhoarding” –  collecting green cones in the fall (up to 15,000 or more) and storing them in one place (generally in the middle of their territory) where they are fiercely protected. A large pile (midden) can result, under which new cones are placed. This cool, moist environment keeps the cones sealed, protecting the seeds from being eaten by mammals and insects that are unable to open the cones.  Middens can contain enough food to last one to two seasons. (Photo: Exceptionally large Red Squirrel midden submitted by Steve Bird of the Coastal Mountains Land Trust, Belfast, Maine)

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Colorful Cottontail & Hare Urine

With snow on the ground, it becomes evident that the urine of Eastern Cottontails, New England Cottontails and Snowshoe Hares is occasionally colored red or blue!  This is not indicative of disease — it is a result of their diet. 

Phytochemicals are responsible for this oddity. Plants contain compounds that contribute to the plants’ color, taste and smell. When the plants are eaten by a rabbit or hare, these compounds pass through the animal’s system and come out in its urine, affecting the urine’s color. I am not aware of which plants produce the more commonly seen red urine, but compounds in the twigs and bark (the fruit is not often eaten by hares and rabbits) of the invasive European Buckthorn (Rhamnus cathartica) can turn rabbit and hare urine blue. (Initially the urine is yellow, but after about ten minutes’ exposure to the sun, it turns blue.) 

As winter progresses, your chances of seeing blue urine increase, as much of the easily accessible nutritious food has been harvested and rabbits and hares resort to eating the less desirable twigs and bark of European Buckthorn. (Photo: Snowshoe Hare tracks and urine)

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New Children’s Book Release

My 14th children’s book, Animal Homes, has just been published. It takes a look at the homes of creatures large and small — where they are built, what they are made of, how they are constructed and the ways in which they suit the needs of the animals that inhabit them. From the lodge of a beaver to the bubble home of a young spittlebug, children 4 – 8+ can compare their home with those of others. Copies may be ordered online and in independent bookstores. (For those who follow my family, Sadie, Otis and Lily Piper are featured in their home on the last page!)

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Birds Gathering Grit On Dirt Roads & Roadsides

Birds compensate for their lack of teeth with a two-parted stomach, the first of which (proventriculus) secretes digestive enzymes and the second of which (a muscular gizzard) grinds the food they’ve eaten into small digestible bits.  Birds that eat hard seeds and nuts tend to have thick, muscular gizzards, while those species that eat very easily-digested foods such as soft-bodied insects, soft fruits, or nectar often have very small and thin-walled gizzards.  Many birds whose diet consists of hard substances, including seed-eaters, swallow grit (often why you see them on dirt roads or the sides of plowed roads where dirt has been exposed) to enhance the gizzard’s ability to pulverize food.

At this time of year, American Goldfinches, Common Redpolls, Snow Buntings, Tree Sparrows and Eastern Bluebirds (among others) can be found swallowing roadside grit to help grind up the seeds that they consume.  (Photo:  While a majority of their summer diet is insects, Eastern Bluebirds consume many fruits (containing hard seeds) during the winter, a change in diet that allows them to remain in northern New England throughout the year.)

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Muskrats Foraging

Usually at this time of year, Muskrats are restricted to foraging beneath the ice and eating their mostly herbivorous diet inside “push-ups” — huts made out of excavated vegetation that have been hollowed out and serve as protective outposts where they can eat and rest. Because of warmer weather this winter, many ponds have retained open areas where Muskrats (and Beavers) can climb out of the water and enjoy sunshine (if they’re lucky) and fresh air while they eat.

Unlike Beavers, which store their winter food in a pile adjacent to their lodges in the fall, Muskrats forage for food on a daily basis throughout the winter. While occasionally they eat small fish, clams, snails and turtles, Muskrats’ preferred diet is the roots, stems, leaves, and fruits of many water plants, such as cattail, water lilies, and rushes. Equipped with a thick, waterproof coat of hair, they are capable of remaining submerged up to 15 minutes collecting food due to a decreased heart rate and oxygen stored in their muscles.

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Snow Buntings Feeding

Congratulations to Kathie Fiveash, the first NC reader to correctly identify the tracks and feeding sign in the latest Mystery Photo as those of Snow Buntings (Plectrophenax nivalis).  These birds began arriving in the northern half of the United States from their summer home on the northern tundra last fall and will remain here until March, when they begin migrating back to their breeding grounds.

In the winter, 97% of a Snow Bunting’s diet is weed seeds, including those of knotweed, ragweed, amaranth, aster, goldenrod, grasses and grains. These birds forage on the ground, collecting seeds from the protruding stems of tall weeds, occasionally reaching or leaping up to take seeds from taller stems, jumping against stems to scatter seeds or bending stems over by stepping on them. (Birds of the World, Cornell Laboratory of Ornithology)

While foraging, Snow Bunting flocks are constantly restless, frequently flushing rapidly and low over the ground for short distances.  A flurry of birds, much like snowflakes, fills the air nearest the ground for a few seconds while they relocate to a new area. Birds at the back of the flock fly forward to the front, creating the impression that the flock is rolling along.

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Mystery Photo

If you think you know who has been feeding here, go to the Naturally Curious blog (www.naturallycuriouswithmaryholland.wordpress.com) and enter your answer under “Comments.” (Hint: photo taken in large agricultural field in Champlain Valley of Vermont.) Answer will be revealed on Monday, January 11. (Difficulty 1-10 = 10)

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What Determines The Internal Air Temperature Of An Active Beaver Lodge In Winter?

Regardless of the outside temperature, the interior of occupied beaver lodges has a fairly stable temperature of about 32°F.  This is due to several factors, one of which is insulation. Beavers spend much of the fall collecting and stuffing mud into the cracks between the branches that provide a framework for their lodge (leaving a mud-free air vent at the top of the lodge).  This mud as well as any snowfall that occurs during the winter help keep out the cold and retain the warmth that the resident beavers’ bodies radiate. 

A comparison of the (cooler) interior temperature of bank dens and that of open-water lodges confirms that the temperature of the substrate underlying a lodge also contributes to the air temperature of the chamber.

Lastly, heat produced by beavers raises the temperature of a lodge above that derived from the lodge substrate.

(Photo: beaver lodge on a morning cold enough to show “beaver breath” escaping through the air vent that runs up through the center of the lodge to its peak. Thanks to Kay Shumway for photo op.)

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Fish are a primary, but not exclusive, food source for Bald Eagles

Hands down, Bald Eagles (like the 2nd year immature bird pictured) prefer fish over other prey — roughly 56% of the diet of nesting Bald Eagles consists of fish such as salmon, herring, shad, and catfish.  However, eagles are opportunistic foragers and over 400 species of prey have been recorded, half of which are waterbirds. Reptiles, amphibians, invertebrates such as crabs and crayfish, and small mammals such as squirrels, rabbits, muskrats, young beavers, fawns and raccoons are also subject to Bald Eagle predation.

During their first year, until they learn to be proficient hunters, Bald Eagles frequently feed on carrion. Even as adults, eagles regularly consume roadkills and deer that have died as a result of being stranded on ice. Whatever food is available and requires the least amount of energy to capture is usually high on their list.

Although not considered a primary source of food, domestic pets are subject to occasional predation by eagles. A discovery made by Fish & Wildlife personnel engaged in banding Bald Eagle nestlings may be of interest to cat owners who allow their pets to roam free in the great outdoors.  Upon reaching one nest, they found, among the detritus, over 20 cat collars.

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Paper Birch Seeds Dispersing

Paper Birch (Betula papyrifera), also called White Birch, produces separate male and female flowers on the same tree, both in the form of catkins (cylindrical clusters of flowers). The catkins form in the fall and overwinter in a dormant state. In the spring they mature as the leaves develop, becoming pendulous. Male catkins are 2-4 inches long, whereas female catkins are usually 1–2 inches long. Both male and female flowers lack petals, enhancing wind pollination. After fertilization occurs, the male catkins wither away, while the female catkins droop downward and become cone-like.

The mature female catkins consist of tiny winged nutlets that are located behind three-lobed, hardened, modified leaves called bracts. Both winged seeds and bracts are usually dispersed by the wind during the fall and early winter. Birch bracts are species-specific — different species of birch have different-shaped bracts, allowing one to identify the species of birch that a bract comes from. Those of Paper Birch (pictured) look somewhat like soaring birds.

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Where Do Foxes Sleep In The Winter?

If you pick up just about any book on Red Fox behavior, you will read that as a general rule they do not seek shelter when they sleep, even during cold winter nights. They are more apt to sleep in an open, exposed area unless the wind is blowing hard, in which case they will find a protected spot such as their den (see inset). In most winter conditions they typically choose a slightly elevated patch of ground, curl up in a ball, tuck their noses under their tails and sleep with nothing more between them and the elements than a dense coat of hair.  

When they sleep, foxes only do so for 15 – 25 seconds at a time, waking up and looking around before going back to sleep.  In dense cover, a fox allows itself to go into a deeper sleep, waking every hour or so to look and listen for potential danger. (Photos: Red Fox bed at base of tree; (inset) Red Fox den, revisited after the first winter storm.)

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