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Archive for February, 2021

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.

Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com  and click on the yellow “donate” button.