Mysteries Abound

Studying nature, the answers we find lead often to more questions. Mysteries abound, such that naturalists and ecologists frequently act as sleuths in pursuit of clues. Observations feed our curiosity, leading to speculation, reflection, and inquiry.

So I was naturally curious when one of our canoe-program volunteers mentioned that he had seen some unusual markings along the bank of the Kishwaukee River in the Deer Run Forest Preserve. He said it looked like someone had dragged something out of the brush and into the river. When he told me about it, he was helping out with our youth canoe camp, Blazing Paddles. We were going to be paddling that very section of the river and he wanted to know if I could help interpret what had made the marks.

As good fortune would have it, he was able to point out the place along the bank shortly before we directed our pod of teenaged paddlers to pull ashore for a lunch break.

striations, etched like scratch marks into the sloping riverbank

striations, etched like scratch marks into the sloping riverbank

With a small band of curious campers in tow, I hiked back along the shore to investigate. The markings fanned out from a small opening in the vegetation, as if someone had combed or raked the surface. But this was no Zen garden and there were no trails near this section of shoreline. I ducked into the willows to investigate further.

There, behind the edge of the brush line, the answer was apparent. Sharp stumps of willow, a couple of inches in diameter, bore the grooved channels formed by sharp rodent teeth. Beavers apparently had been taking down willows and dragging them toward the water, stump-first with the upper leaves and branches trailing, raking the surface of the soil.

The adolescent paddlers in my company were impressed, never before having seen for themselves that sort of evidence of beaver activity—and they also were impressed with the beavers’ famed industriousness. We knew that the work must have been recent, as we found additional evidence farther along the bank:  A length of willow trunk, gnawed at the base and bearing the tell-tale tooth marks, still had a few green leaves at the tip. Those leaves would have wilted within days of the stem having been severed.

evidence of beaver activity; adolescent human for scale

evidence of beaver activity; adolescent human for scale

Beavers (Castor canadensis) are the largest rodents in North America, with bodies reaching 30 inches or more in length. A typical adult beaver may weigh between 35 and 65 pounds, although specimens weighing up to 85 pounds have been reported. Beaver teeth are formidable: the front incisors are oversized and appear orange in color, as iron replaces calcium in the enamel, making the incisors exceptionally strong—capable of gnawing through hardwood trees.

a stump exhibiting the grooved marks left by a beaver’s tough incisors

a stump exhibiting the grooved marks left by a beaver’s tough incisors

Further adaptations of these aquatic mammals include webbing between the toes of the hind feet and the distinctive paddle-like tails. When startled, a beaver may slap its flat tail in warning as it disappears beneath the water’s surface. Beaver fur was prized by the trappers who were among the first Europeans to explore this area. The outer guard hairs are long and glossy while the underfur is very fine and dense, protecting and insulating beavers’ skin from the water. Oils secreted through glands are distributed and combed through the fur while grooming to enhance the waterproof qualities of the fur. Such musky oils are also used to mark territorial boundaries.

Physiological adaptations like webbed feet and a flat tail enable beavers to thrive in aquatic environments.

Physiological adaptations like webbed feet and a flat tail enable beavers to thrive in aquatic environments.

Beavers are monogamous and live in extended family units, typically spanning three generations. Their preferred diet consists of herbaceous vegetation, although they will browse on woody stems when necessary.

Of course, we seldom see beavers. Not only are they generally restricted to riparian and pond-side habitats, they also are generally nocturnal, spending the daylight hours in lodges built of branches and accessible through underwater entrances. So, like much of the wildlife with whom we share this little corner of the planet, they may remain unseen, but can be known by their effects.

And beavers can have amazing effects on the environment. They are nature’s environmental engineers; their dams and lodges my redirect the flow of streams and rivers, flooding vast areas and influencing plant communities and habitats over long periods of time.

Nature is endlessly fascinating; collecting evidence, we are drawn deeper into explorations of interrelated phenomenon. Threads lead to nodes that branch off to other threads. One of the things that I find satisfying about studying nature is that we can devote a lifetime of study there and never get to the end of it all. Mysteries abound and there is always more to explore.

Home Sweet Home

Home. Such a simple, yet evocative word. So essential to our sense of security and wellbeing. Most of us rely pretty heavily on the comforts of home to help us endure the vicissitudes of life out there in the wide world. Faced with daunting challenges and fearful prospects, dangers, difficulties and dilemmas, the child within cries, “I wanna go home!”

We are not alone in finding safety and comfort in the nest, in the den, in the burrow. Our animal compatriots in the wild need their space also. Educators here at Severson Dells explain to school groups that organisms “Have to Have a Habitat” and we explore the many ways in which they find their respective niches in nature. Every organism needs shelter, nourishment (food and water), and space. If any of those needs is withheld, the organism cannot thrive and may not survive—at least not for long.

I was reminded of these essential truths recently when setting up a photographic plot to record progress in restoration here at The Dells. Along the crest of a low ridge, I came across a spoil pile:  light-brown glacial till unearthed from below the surface by an animal digging a burrow or den. Evidently, the animal had taken up residence there some time ago:  the soil was worn and lightly weathered; new plants had taken root there.

Outside this burrow, the spoil pile has been colonized by new plants.

Outside this burrow, the spoil pile has been colonized by new plants.

Just a few feet away, however, was a second excavation, one that apparently was quite fresh, looking as if it had never seen rain. What impressed me about it was the size of the stones that had been dragged or pushed out of the hole. Some were rough-hewn, several inches in diameter, and must have weighed a few pounds.

a new spoil pile of glacial till featuring large stones unearthed from below

a new spoil pile of glacial till featuring large stones unearthed from below

It can be difficult to tell with certainty which local mammal would have dug a given burrow. For denning season, coyotes may dig holes to occupy while giving birth and caring for their young pups, although such dens are generally abandoned by early July. Opportunistic as they are, coyotes are more likely to use a den that was excavated, and subsequently abandoned, by another animal. Red foxes typically leave scraps of bone and hide around a den entrance. Woodchucks (groundhogs) are well known for their excavation expertise and their dens often feature a “dirt porch.” A woodchuck would be capable of pushing a fairly large stone up and out of its burrow.

Curiously, a number of local animals may occupy a single burrow, either consecutively or—reportedly—even at once. Skunks, opossums, badgers, coyotes, raccoons, and groundhogs are said to be among those known to cohabitate from time to time.

Hollow trees, of course, offer another familiar form of shelter for wildlife. A large oak near the underground burrows presented an ample opening into an interior chamber; a walnut husk on the lip of the opening hinted at the chamber’s occupancy.

another residential address for local wildlife

another residential address for local wildlife

In addition to the many bird species known to be cavity nesters, the following mammal species also are known to occupy hollow trees:  raccoons, opossums, fox squirrels, gray squirrels, flying squirrels, bats, white-footed mice, bobcats, and gray foxes. (Yes, gray foxes do climb trees!) Given the walnut husk, it seems likely that one of the squirrels calls this place home.

Home. It means much more than the house (or den or burrow or nest) that we live in. Home embraces the wider environment. Our community. And when we care deeply about the natural environment, we come to realize and respect the fact that our home includes at least a portion of the natural world. And we associate our sense of comfort and wellbeing with that local environment. This is what it means to have developed a sense of place. And this is what it means to come home to nature.

Shrewd Observatons

As one of our volunteers and I were standing at the window this morning, watching the birds at the feeders (he was hoping for some redpolls), I saw a small, dark, furry body scamper across the snow toward the sunflower seed hulls scattered on the ground.  As quickly as it appeared, it disappeared behind a pile of snow. 

“A vole!” I declared.  Then I corrected myself.  “No, a short-tailed shrew!”

Neil put up his binocs as the animal reappeared, continuing its foray toward the motherload, and indeed, it was a shrew.  Blarina brevicauda – the only venomous mammal in North America (technically there are two species, the northern and the southern short-tails, but for the purpose of the article, I shall lump them together).

shrew crop1.jpg

Now I know what you are thinking:  venomous mammals?  Really?  Truly!  There are not many worldwide:  the duck-billed platypus, the Cuban and Haitian solenodons (which are foot-long, shrew-like animals), the Eurasian water shrew, and the short-tails.  Unlike the others, the platypus isn’t going around biting and “poisoning” animals – it has a spur on its hind foot that it uses in self-defense to inject venom into its enemies; the rest of them, however, use their venom to incapacitate their prey.

If you came out to our Science Saturday last month, you would’ve seen a short-tailed shrew specimen at the table where we were talking about the subnivean zone, for these small mammals are active all winter, scurrying around between the ground and the snow layer in a constant search for food.  Their metabolism is so fast that they must eat every two or three hours or else starve to death.  Therefore, they do not hibernate, and they are constantly on the move.  Invertebrates (insects, worms) make up the bulk of their diet, but thanks to their venomous bite, they can also immobilize mice and voles, taking them into their tunnels to consume later at their leisure (if such frenetic animals are ever “at leisure”).

What kind of venom are we talking about?  Is it dangerous to people?  What if one bites my cat, my dog, my kid?

The shrew’s venom is apparently similar to that of the cobra, chemical-wise.  It contains two kinds of toxins:  a neurotoxin that causes paralysis, and a hemotoxin that decreases the prey’s blood pressure and wreaks havoc on the circulatory system.  It seems that the shrew’s “purpose” for applying the toxin is not so much to kill its prey (for it is fully equipped tooth- and claw-wise to take out most of the food it finds), but rather to allow it to put prey into storage for later consumption – a paralyzed beetle or mouse will stay “fresh in the larder” until needed later on, when perhaps a quick snack cannot been found.

Knowing all that, you might still be worried about Fluffy, Fido or Freddy.  But fear not – if your cat or dog is bitten by a shrew, it will most likely not come to any harm.  Infection from the bite is probably of more concern than any reaction to the toxin.  Ditto for your child. 

Many years ago, I took a class on Winter Mammalian Ecology, and the guest instructor was Dr. Joe Merritt, who probably knows more about short-tailed shrews than anyone, thanks to his years of research at the Powdermill Biological Station in Rector, PA.  He claims to have been bitten many times by his research subjects, and has suffered little more reaction than what one would get from a bee sting.  However, like with bee stings, some people can react more strongly than others, so it is always wise to not handle wildlife unless it is absolutely necessary, and even then, use proper care and precautions (wear gloves).

shrew crop2.jpg

But I love these little guys.  They are energetic, easy to sneak up on (I was within a couple feet when I took these photos), they sing (yes – many years ago I heard one singing in the backyard while I was sitting on the grass, writing in my journal).  They have tiny little eyes, no external ear flaps, and fur that is unidirectional – all adaptations for a life spent primarily underground.

I have found many a dead shrew just lying on top of the ground in my lifetime.  Found two within about 15 feet of each other last summer right here in Rockford while I was walking the dog around our neighborhood.  Short-tailed shrews are very common (living ones, I mean, although deceased ones seem to be quite common, too).  I have often wondered why these small morsels remain uneaten by the predators that caught/killed them, and later on by scavengers, and after a bit of research I learned that birds will eat them (owls, hawks), but not so much mammals.  Supposedly this is because the shrews taste bad (and birds, apparently, are oblivious to this).  This could be from glandular secretions (located on the animal’s belly and nether regions), which turn a tasty mouthful into something that makes the predator (say a fox, or house cat) think twice about actually consuming it.

If you didn’t get to see the shrews last month, don’t fret the missed opportunity.  I have sent all the bodies from my freezer to a taxidermist and in a couple months I anticipate having specimens on hand to share with visitors.  In the meantime, keep your eyes peeled.  Watch for small furry bodies moving along the foundation of your house, or darting out to your birdfeeders.  Look for a pointy snout and plush grey fur.  Odds are, short-tails are in your back yard and you’ve just never had the opportunity to say hello.