Saturday, December 28, 2013

Black and White

Frosty air stung my cheeks and my breath froze to my eyelashes as I zoomed down the trail. Fading sunlight and frigid temperatures haven’t kept me from skiing! An intricate pattern of blacks and whites decorated the thick winter woods. Each twig carried a shadow of white snow. Wind-driven snow accentuated the furrowed bark of trees.  Subtle shadows graced the drifted terrain. I was skiing through an Ansel Adams photograph.

The pale sunlight gradually faded behind the hills, and a gibbous moon rose to take its place. I barely noticed the change at first, since the moon (reflecting light from the sun back toward us) was so bright. During the long days of summer—when bedtime comes before twilight, and mosquitoes flock at dusk—I seldom get outside after dark. Skiing under the stars, with trees casting moon shadows across my path, was a lovely treat. The contrast of trees and snow made it easy to navigate. I left my headlamp in my pocket.

As my purple-mitten clad hands swung in an easy rhythm, I noticed their color fading toward charcoal gray, finally matching the color scheme of the forest. Despite being mostly limited to seeing in grayscale now, it was still impressive that I could see at all. According to the American Optometric Association (AOA), the sensing capabilities of the human eye reach across nine orders of magnitude. This means that the darkest light we can see is one-billionth as bright as the brightest light we can see.

Two different types of light receptors in our eyes make this possible. Our cone cells function in daylight, and give us color vision with a high resolution of detail (20/20 vision if we’re lucky). Rod cells work even in very dim light, but provide limited resolution (20/200 vision), and a black and white palate. Cones are clustered in the center of our retinas, while rods form a donut around the periphery of the retina.

(A freaky side effect of our rod and cone arrangement is that if you stare directly at a small object in the dark, it will disappear! A tree trunk might be severed with its top half floating, your friend’s face might go dark, or a star you just saw might blink out. These optical illusions are caused by a small blind spot in the middle of our night vision, where the cones would normally focus if they had sufficient light. If you just look slightly to the side, the objects will reappear.)

Humans have several additional adaptions that help us to see across such a wide spectrum of light levels. Our pupils can dilate to let in more light at night, or contract to physically protect our eyes from damaging amounts of light during the day. The diameter of the pupil can contract to 1.5mm and expand to 8mm, which equates to a 30-fold range in the quantity of light entering the eye. After skiing for more than half an hour in low light conditions, my pupils were probably widely dilated.

A chemical called rhodopsin is another key to our night vision. Rods use rhodopsin to absorb photons and perceive light by converting it to electrical activity, which initiates visual impulses in the brain. (Cones use their own specific photopigment in the same way.)
When you expose your eyes to bright light, photons actually split the rhodopsin into two other chemicals. This reduces the sensitivity of our retina and protects our eyes from damage to intense light. It also diminishes our ability to see in low light. (Have you ever noticed how turning on a flashlight temporarily ruins your night vision?) Although it takes several minutes, the chemicals eventually recombine into rhodopsin and our night vision returns.

The moonlight provided plenty of light for skiing. Rods can function even on an overcast night with no moon, and the high contrast between snow and trees gave me confidence in avoiding collisions. As moon shadows from the trees slipped by under my skis, I looked down to admire the patterns. I was surprised to find that my skis still looked red!

Back inside, I did a little research and discovered that with any color except red, as you turn down the lights, you can watch as first the color turns gray (cones stop working), and then you lose the sensation of light (rods stop working). This is called the photochromatic interval. With red, however, the color and sensation of light disappear at the same time. And, as it turns out, cones can function a little even with only 50% moonlight!

As wonderful as human vision is to me, I know that many animals see in ways that we can only imagine. Many critters have better night vision, can see more colors than we do, and can even see faster than humans. I will explore those super senses in a future article.

With Winter Solstice and the shortest days of the year behind us, we’ll soon have increasing amounts of light to see by. For now, our grayscale night vision melds perfectly with the black and white winter world. By summer, when our cones have 15 hours and 43 minutes of daylight to see by, the Northwoods will once again be full of color.

Friday, December 27, 2013

A Visit to the Hawkeye State

My journey home for the holidays used to mean a cross-country flight. Since I moved back to the Midwest, it means a long drive over some of the most beautiful rural highways in Wisconsin, Minnesota, and Iowa. Long ago, my dad entertained us on similar car trips by watching for raptors all across the Hawkeye State.

Red-tails on power lines, kestrels on road signs, harriers soaring over fields, eagles near the river, and owls on fence posts captured our attention. If the traffic was light and a field driveway was near, Dad would “flip a Louie,” get out his camera with the long lens (nicknamed “Big Bertha,”) and go back to see if he could get a good shot. We’d hold our breath and try not to wiggle the car. Sometimes the raptor was cooperative, and posed for a while, blinking in the sun. Sometimes they took off just as Dad was about to push the trigger on the motor drive.

My trip home for the holidays this year included many raptor sightings, and while I didn’t do any U-turns to photograph them, I admired their calm grace and their high hunting posts in roadside trees. It is hard to believe that birds of prey could be looking for mice from way up there, but I know they can see between four and eight times as well as us humans. According to one source, “If you swapped your eyes for an eagle's, you could see an ant crawling on the ground from the roof of a 10-story building.”

How do they do that?

Accommodation is one trick birds use to focus on objects at a variety of distances. This simply means that tiny muscles around the eye alter the curve of the lens so that it can focus on objects that are far or near. It’s like using the focus wheel on binoculars. Humans share this adaptation for focusing. You may have noticed the time-delayed focus as you stare at an object to see it better and your muscles automatically curve the lens after a second. The amazing thing about raptors is that they can change the shaped of their cornea as well as their lens. This gives them an even more precise focus on the world.

I experienced the lack of accommodation when my holiday journey detoured to the eye doctor’s for my annual checkup. As I sat in the waiting room waiting for the drops to finish dilating my eyes, I noticed that I was having increasing difficulty reading the magazine. I asked, and Dr. Landis explained, that the numbing drops don’t just stop the muscles around my pupils from working, they also stop my accommodation muscles from working.

While squinting in the bright snow and frustrated at blurred vision on the way home from town, I was still able to spot a rough-legged hawk soaring over the corn stubble. Their feathered or “rough” legs are well suited for both summers in the Arctic, and the relatively mild winters of Iowa. Hunting on the wing presents some challenges, though, and I can’t imagine being able to see details on the ground from such a height. Raptors and other birds not only use muscles to focus their eyes, they also have more light-receptor cells to focus the images on.

Humans have a fovea, or focal point, at the center of our retina with 200,000 light-receiving cone cells per millimeter. This provides for our good color vision. Eagles (and other raptors), on the other hand, have about a million cones per millimeter in their central fovea. That gives them much higher resolution vision. Not only is their fovea packed more densely with cones, it is also deeper than ours, so it may act like a telephoto lens and give them extra magnification in the center of their field of view.

Moreover, raptors actually have TWO fovea. In addition to their central concentration of cones, they have a lateral fovea that allows them to keep the horizon and the ground in focus simultaneously.

All this extra visual resolution gives hawks and eagles somewhere between 20/5 and 20/2 vision. At best, the physical properties of human eyeballs limit us to 20/10 or 20/8 vision. In other words, what a normal person could see at eight feet, an exceptional person could see at twenty feet. Or, what a normal person could see at TWO feet, a hawk could see at TWENTY feet.

Scientists consider bird vision to be the finest in the animal kingdom, and raptors are at the top of their class. But raptors don’t lead the class in every respect. Smaller birds may see faster than raptors, and receive more colors. Migratory birds may be able to see polarized light and the Earth’s magnetic field. While owls are raptors, and do have excellent eyesight, their eyes are tuned for night vision.

Over the holiday, eagles and hawks soared past our windows on a regular basis. Each time, several sets of human eyes focused eagerly on the majestic visitor, still registering barely more than a blur of flight. It is fun to imagine just how differently various creatures can see the world. Wouldn’t it be fun if we could truly be in the hawk eye state?

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, December 13, 2013

There is No Place Like Home

Uncountable stars twinkled brightly as I stepped into the night. Head tilted back, I reveled in a moment of wonder. The fingernail Moon hung among the stars—a tiny sliver of light in the Universe. Venus, named after the Roman goddess of love and beauty, shone brightly just below the moon. As I inhaled deeply, my nostrils froze together, and the cold, dry air in my throat triggered a coughing fit. There went my moment of awe!

Winter stargazing means clear skies and frigid temperatures. The clearest nights are also the coldest. Why? All day, the Earth absorbs energy from the Sun through visible and infrared light. Blacktop roads soak up rays, dark trees warm up, even pale snow captures a little bit of the Sun’s energy. Then, all night long, the Earth radiates heat back up toward the sky.

Clouds are very efficient blankets for our planet. They can trap heat and radiate it back down toward the Earth. If there are no clouds, however, the heat escapes. So, clear nights get colder. In addition, cold air can’t hold as much moisture as warm air, so the number of water molecules standing between our eyes and the stars is reduced even further.

All of this makes winter a great time for contemplating Earth’s place in the Universe. Why are we standing here instead of on Venus or Mars? What makes the Earth special?

First, consider the Moon. While we might think of our Moon as just a lowly satellite revolving around us, it has been integral to the history of our planet. The Moon stabilizes the Earth’s rotation, which keeps our seasons (caused by a slight tilt of the Earth), from going to the extremes. Even its formation was important. Long ago (scientists think), collisions with asteroids flung lighter material away from the Earth, where they coalesced into the Moon. This means that our core is much denser than that of Venus. Today, Venus’s lower density means that its interior is entirely liquid, and oddly calm.

In contrast, the denser Earth has a swirling core that is part liquid and part solid. The movement of our core generates the Earth’s magnetic field. Without our magnetic field, we would be bombarded by harmful radiation from the Sun. Without a magnetic field, solar radiation drove away the water on Venus.

So, instead of fluffy white clouds of water vapor, Venus has opaque clouds of sulfuric acid, and a runaway greenhouse effect. (You could never stargaze on Venus!) The average temperature on Venus is now 864 degrees Fahrenheit. That almost sounds inviting when our mercury dips below zero!

Mars, on the other side, has a different problem. Mars's atmosphere is about 100 times thinner than Earth's, so it lacks a thermal blanket. The stars might always be bright on Mars, but the nights are always cold. During the day, the temperatures on Mars can reach a balmy 70 degrees Fahrenheit. However, its average temperature is -80 degrees, and the night-time poles can dip to -225 degrees.

What factors led to our “just right” temperatures and atmosphere? Our mass (not too big and hot like Jupiter, not too small and cold like Mars) is one parameter. The gravity on Earth doesn’t just press us back into our beds in the morning; it also tugs at the atmospheric blanket and prevents it from slipping away. Mars has a smaller mass than the Earth, and therefore lacks sufficient gravity to hold onto its atmosphere.

Our distance from the Sun is also ideal, since it partly controls how much radiation we get from our closest star. Not too far, not too close, we got it just right.
“…dear star, that just happens to be where you are in the universe to keep us from ever-darkness, to ease us with warm touching, to hold us in the great hands of light…” –Mary Oliver, from “Why I Wake Early.”
In the end, almost all the factors that make the Earth special relate to the presence of liquid water, and our ability to retain it. Liquid water, and the seasonal presence of solid-state water (hooray for fishable ice and skiable snow!), are certainly important in my life!

On that starry night, the scarcity of liquid water above me was both a blessing and a curse. The chance to gaze out at the sparkling Universe emphasized that there is no place like home…even if home is where your nostrils freeze together.

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Night Magic

Headlamp stretched over wool hat, I strapped on snowshoes (fresh from basement storage) and ventured into the snowy dark.

A few flakes glittered through the air, but mostly the snow clung to trees and heaped on the ground. My light reflected brightly off white in all directions as I walked along in its bubble. The only sounds came from my snowshoes--creaking, squeaking, and shuffling.

Trees leaned out over the driveway, reaching their ice-encased, snow-frosted twigs toward my path. The lower edges of the iced twigs were scalloped with frozen droplets. Falling temperatures had slowed the drips to stillness. Unable to resist, I licked some fluffy snow-frosting off a birch twig.

Amazed at the beauty caught in every movement of my headlamp, I swept the light around in a wider arc, taking in the intricate patterns of twigs, needles, and snow. A ways off in an open area, the light caught something brighter. Two green eyes shone back at me.

Eyeshine is caused by a layer of tissue called the tapetum lucidum (which means “bright tapestry” in Latin). This layer sits behind the retina, and increases the light available to the animal’s photoreceptors by reflecting visible light back through the retina. Deep sea creatures and nocturnal animals use the tapetum lucidum to increase their night vision.

I was hoping that the two green orbs belonged to the neighborhood bobcat, but as the eyes moved, I could just barely make out the profile of a deer against the snow. Even so, I couldn’t stop my brain from imagining a monster or goblin behind those glowing spheres.

Undaunted by my overactive imagination, I followed a wandering herd of snowed-in deer tracks out the driveway and onto the trail. A snow-laden balsam arched across the trail at waist height, its tip buried under the crust. I gently swung it forward like a gate, and entered a tunnel fit for dwarves

This section of trail sneaks through a thicket of balsam on an old road grade. It is always dark and narrow. Tonight, snowy balsam branches hung especially low and close as I bent down to shuffle through. The passageway heightened my sense of expectation and suspense, as if I really might pop out into the Narnian Empire at any time.

Instead, the trail entered a spacious hemlock grove. As the trees opened up, the dark closed in. Through the open understory, I caught the shining green eyes of four more deer. As they bounded away, a soft whisper of wind tinkled through the treetops. Snowflakes drifted down. The whisper crescendoed to a rush of air, and bigger clumps of snow fell, plopping all around me. As I put up my hood and leaned toward the trunk of a large hemlock, I imagined Ents in a snowball fight. When the dull thumps of falling snow had subsided, I continued on through the aftermath of drifting clouds of crystals.

A cute string of mouse tracks made me grateful for another sign of life. Most small mammals are hiding out under the thick, fresh snow, where a new world has just developed beneath our feet. This ephemeral habitat is called the subnivean layer.

The subnivean layer, like so much of life on Earth, owes its existence to the unique chemistry of water. When frozen, water becomes light and airy, a wonderful insulator. Just as down feathers in your jacket trap a layer of air next to your body, retaining the heat you radiate, a six-inch layer of snow traps air that retains heat from the Earth.

Because of this insulation and radiating heat, a thin zone opens up under the snow, right at the surface of the ground, which stays at a pretty stable 32 degrees Fahrenheit. This becomes even more important as the temperature plunges into the single digits, and then below zero. Without snow to insulate the ground, frost burrows more deeply.

Tree roots, invertebrates, and the myriad little critters in the upper reaches of the soil suffer in cold, dry winters. Snow provides not only provides warmth, it also facilitates easy access to food, and gives cover from predators. “To the mouse, snow means freedom from want and fear,” wrote Aldo Leopold in A Sand County Almanac.

Red squirrels also use the subnivean layer to escape want and fear. In the fall, they cache seeds near the ground, and then use their great sense of smell to find them again, even below four meters of snow. During cold spells, squirrels will dig themselves a little snow den and hang out near their pantry, safe from the searching eyes of predators. I stepped over a small hole excavated by a hungry squirrel, and peeked down into the dry, leafy carpet of the subnivean zone. His tracks still ran across the top of the snow, but with temperature forecasted to plunge, my guess is that he will take a dive, too.

I emerged from the woods onto the gravel road and turned off my light. The world went gray. A grove of balsams—their drooping branches and conical shape perfectly adapted to the heavy snow—stood like statues in the White Witch’s courtyard. A rosy-pink glow in the northern sky gave an otherworldly aura to the night.

Beams of warm yellow light beckoned me back inside, but I hesitated, reluctant to leave this magical world (my snowy backyard) behind.

“And if you have not been enchanted by this adventure-Your life-What would do for you?” –Mary Oliver

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Minerals all around us

Is it frozen yet? Every morning for the past few weeks, I’ve peered into the gray dawn, looking for the absence of waves on the lake. If there wasn’t a choppy surface, then I stared harder still, trying to determine if the reflection was due to calm water, or a skim of ice. One morning the pink clouds reflected on both ice and liquid, as a thin sheet filled my bay. The next morning, I couldn’t see any open water.

I gave the ice another frigid day and night before venturing down to its edge. Wind had piled that first layer of ice up against the shore, and now the round pancakes of ice chunks were frozen together in a jumbled mess. Cautiously, I stepped out away from the shore, and stopped a minute to listen for cracking, and feel for shifting. Solid. I shuffled out toward the smooth ice.

Two inches of clear ice covered the deeper water. Silvery bubbles and crystalline patterns decorated the black surface. Just under the ice, little blobs of mint-green algae bobbed gently, barely moving in a gentle current. Even as the ice was freezing, these little producers had been carrying out photosynthesis and releasing oxygen bubbles, which left shimmering vertical paths in the ice as they rose toward (but never reaching) the surface.

Strange as it may seem, the surface of my lake has just become a mineral. Mineral is a geologic term, describing solid substances with certain characteristics. Minerals are all around us, but mostly overlooked. Let’s take a closer look at ice to see how it fits.

The first criterion in the definition of a mineral is that it must be a natural occurring, inorganic substance. The ice on my lake is natural occurring, of course, but the ice cubes in my freezer are not. Diamonds made in laboratories are not technically minerals, either. Ice doesn’t contain carbon and is not derived from living things, which means it is also inorganic.

Minerals must be crystalline solids, meaning that they have to have an orderly internal arrangement of atoms. This means that water is not a mineral, the same way that volcanic lava is not a mineral, since they are both liquids. As they cool, though, their molecules arrange themselves into distinct geometric patterns. You can see this in the hexagonal symmetry of snowflakes.

Each mineral is made of a particular mix of chemical elements, and has a definite chemical composition. The chemical composition of ice is, of course, two hydrogen atoms and one oxygen atom per molecule, written as H2O. Apatite, a mineral in your tooth enamel, is more complicated, and contains set amounts of three elements, plus variable amounts of four more.

Speaking of appetite, we are surrounded by minerals not only on a frozen lake, but also at the dinner table (especially if we relax the definition of mineral to include human-altered forms). The salt in your shaker is tiny crystals of the mineral halite (also called sodium chloride, NaCl,). The leavening in your pumpkin bread is sodium bicarbonate (NaHCO3). Both the pumpkin and the turkey contain small amounts of calcium and iron.

As you dig into the food on your plate (ceramic plate containing feldspar and silica), with your grandmother’s set of heirloom flatware (silver) or your regular silverware (made of iron, nickel, molybdenum, chrome, strontium, and neodymium), be careful not to chip a tooth filling (gold)!

Give thanks for the screws (iron and zinc) that hold the feasting table together, the drywall (gypsum) that forms your cozy room, and the insulation (vermiculite) that keeps you warm. Don’t forget the electric wires (copper) that power your light bulbs (tungsten, silica), and the plumbing (copper) that carries the remains of the feast away.

As you settle your stomach onto the couch with a swig of pepto (bismuth), and maybe crack a beer can (aluminum), I encourage you to give minerals a second thought. They are all around us, bringing the beauty of snowflakes, the fun of ice fishing, and the grace of good health.

“When we cut the ripe [pumpkin], should we not give it thanks? And should we not thank the knife also? We do not live in a simple world.”

From “At the River Clarion,” by Mary Oliver.

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Tuesday, November 26, 2013

Inhale beauty. Exhale gratitude.

Sharply cold air flooded my lungs when I stepped outside this morning. A fresh dusting of snow glittered where the morning sun filtered through trees, and that same sun shone on rosy clouds in a blue sky. I took another breath. Inhale beauty. Exhale gratitude.

Crunch…crunch…crunch. With sunflower seeds cupped in my outstretched palm, I walked to a spot in between the thicket of balsam fir trees and the empty bird feeder. The trees were silent – frozen by my movement. The hyperactive hopping of a single chickadee broke the stillness. Within seconds, the whole flock was back.

During the summer, black-capped chickadees focus on their mate and their chicks. Even if I didn’t have to take my feeder down because of the bears, they would not gather like this for a group feast. By late fall, chickadee flocks are well established and ready to defend a winter feeding territory. One territory just happens to include my feeder.

Like wolf packs, chickadee flocks have alpha and beta pairs at the top of the hierarchy, other mated pairs below them, and then unmated juveniles at the bottom. Unlike wolves, the juveniles are not the offspring of pairs in the flock. Instead, their parents kicked them out of their childhood range in the hopes of spreading genetic diversity a little wider.

As I stood there, hand outstretched, I listened to the interactions of the flock. Dominant birds responded with aggressive gargles aimed at lower-ranked birds who got too close, or disputed the ownership of a seed. Researchers have found that the gargler almost always wins the fight. Shy “tseet tseets,” from hidden chickadees maintaining contact with the flock filtered through the thick boughs. Chickadee-dee-dee calls could have been greetings to friends, or warnings about the possible danger of my presence.

The whirr of wing beats also filled the air as chickadees swooped bravely over my head to the empty feeder, then on to perch on the broom handle near the door, to cling to the side of the porch pillar with needle-like toes, and then back to the safety of the fir boughs. None flew to my seed-filled hand, although I hoped very intently.

Why wouldn’t they jump at the chance to eat a few more seeds? In order to maintain their normal 108-degree body temperature, chickadees must eat the caloric equivalent of 250 sunflower seeds each day. They gain up to ten percent of their body weight in fat each day, and burn it off each night to stay warm.

Maybe the chickadees weren’t hungry enough to brave my hand because they were raiding their cached food instead. Norwegian researchers found that the tit, (a chickadee relative,) caches up to 80,000 seeds in a single autumn. Unlike red squirrels, who put all their seeds in one stump and then have to defend them fiercely, chickadees spread out their seeds singly, and don’t worry about a few getting stolen.

If I were a chickadee, my biggest source of seed loss would be my own forgetfulness! Chickadees have it figured out. They use forgetfulness to make space for new memories each year. Each fall, brain neurons containing old information die, and new neurons grow with current information about seed locations, social flocks, and their habitat.

This also means that they have forgotten my past role as a harmless provider of food. My hand throbbed with cold, so I stuck it back in my mitten and walked down to the lake for a break. Those rosy clouds and that blue sky sat reflected in a section of open water, surrounded by a skim of ice.

I continued down the driveway, stepping over the leaping tracks of red squirrels, the tiny bounds of mice, and the snowed-in trail of a midnight fox. All these brave creatures share the winter world with the chickadees and me.

Scooping seeds out from the tip of my mitten where I had stored them, I tried again. Standing silently, hand outstretched, I waited. Again, the flock began swooping around me, but not landing. Then a different movement caught my eye – a vole was foraging at the base of the dead spruce.

The instant that my focus left the chickadees for the vole, I felt the spiny grip of a chickadee on my finger. Not daring to shift my gaze and scare it off, I kept my eye on the vole, and my awareness in that finger. I took a deep breath of crisp air. Inhale beauty. Exhale gratitude.

Now the spell was broken. Several more chickadees swooped down to grab seeds. In between, I was able to look down. One chickadee cocked its head and peered up at me through a shiny black eye, as if to say, “I see you. You’re ok.” That was all I wanted.

“Sometimes I need only to stand wherever I am to be blessed.” 

― from Evidence, by Mary Oliver

It’s Not My Track

Despite the gray skies, despite the chilly wind, I needed a hike. Already, this early winter weather and lengthy darkness has me down. Bike season is over for my sensitive toes, ski season taunts me from just around the corner. I could have curled up on the couch with a book, but I lured myself out to the trail with memories of other times that a walk in the woods has done me good.

An inch of snow covered the grassy, soggy ski trail. Movement felt good, but my mood still clung. Soon, I began noticing tracks: the daisy chain of a grouse’s small steps; the dots and lines of a mouse dragging its tail; the lacy pattern of a shrew’s diagonal walking gait; the funny little half-tunnel of a vole burrowing along the top of the grass.

The large, loping tracks of a fisher made me stop and look. Then, barely ten steps down the trail, the belly-slide marks of an otter made me laugh as I imagined his playful mode of travel.

In summer, the woods bustle with life, but the comings and goings of little feet are hard to decipher in the thick grass and leaves. The first snow primed the forest’s typewriter, and now the paw-and-claw-inked words are preserved for a moment, allowing me to read their stories.

Still, the cabin fever was persistent. Mouse tracks became routine, and above trudging footsteps, my mind turned inward.

Then, out of the corner of my eye…WOLVES! While my thoughts had been elsewhere, my eyes registered the big, four-toed paw prints scuffing the snow across a whole section of trail. I grinned, my mind now alert and senses primed. A quick survey of the scene allowed me to estimate: definitely four, probably five wolves. Mary Oliver’s poem, Bear, comes to mind: “It’s not my track, I say… to no one but myself, since no one is
with me.”

Maybe you think I should be nervous, walking in wolf-filled woods alone. I am not. Having tracked wolves in several different places (Minnesota, Yellowstone, Wisconsin), and observed them for hours on end (they mostly slept), I am confident that their wildness and skittishness of humans keeps me safe.  I am ok with any risk that remains.

Instead of nervous, I am thrilled. I love seeing evidence that such graceful, powerful predators inhabit these woods. I love knowing they are here--running easily, determinedly, playfully through the forest. Perhaps if I had livestock, or dogs, or children I would feel differently. Perhaps that’s why I don’t have them…

When Mary Oliver describes discovering the bear track, she hints at all sorts of reports she’s heard of other people’s bear encounters. Then she goes on to say, “But not one of them told what happened next-I mean, before whatever happens-how the distances light up, how the clouds are the most lovely shapes you have ever seen, how…every leaf on the whole mountain is aflutter.”

After seeing those tracks, I felt alert and alive. For the rest of the hike I peered into the woods. Leaves fluttered. The clouds flushed pink in the setting sun. Nothing else happened. No wolves let me see them.

Too soon, I crossed my own large boot tracks near the trailhead. As I neared my car, I stored this hike away in my memory for use on another day when I need an extra something to lure me out for a walk in the woods.

“In every walk with nature, one receives far more than he [or she!] seeks.” – John Muir

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, November 15, 2013


I love things that help me get a new perspective on the world, so I always request a window seat. Taxiing to the runway, my face pressed to the clear plastic window, I watched a flock of snow buntings swoop in unison above the grass. White flashed on their wings. There was grace in the unconsciousness of their flight.

Birds are so well adapted for travel through the air that their movements can seem effortless. Even when we see how hard they are working, the power in an eagle’s wings and the skill of a hummingbird’s maneuvers fill us with a sense of awe. Human-designed flight was not so easy.

In the years since Icarus flapped his waxy wings toward the sun in ancient Greek mythology (and fell into the ocean when they melted), humans hadn’t had much luck trying to copy birds. Paradoxically, the great success in human flight came when we stopped trying to mimic natural flyers and began designing from scratch, says Professor Spedding, of the University of Southern California.

Now there I was, ready to take to the air, casually fulfilling the dream of flight with millions of other people today. We turned down onto our runway and sped up. As the force pushed me back into the seat, I imagined what it must be like to be a loon – running hard across the lake, splashing and pushing with broad feet, until finally achieving enough speed for liftoff. Even when I was no longer jostled by the bumps of earth, I was still pressed back into my seat by the acceleration.

Loons have the heaviest wing-loading of any flighted bird, so they, like airplanes, must gain speed in order to generate enough lift to leave the ground. They must maintain that speed, too, or risk a crash landing. Have you ever seen a loon fly slowly? Me neither. Also like commercial airliners, loons need their wings mostly for long-distance trips, and use wide-open spaces for take-off and landing. This allows both planes and birds to survive with limited maneuverability.

I’m likewise fascinated to see a bird’s-eye-view of the landscape – to follow familiar rivers, highways, lakeshores and forests in an effort to understand them from a new perspective. Today, however, my view was blocked as we rose through a thick layer of bright white clouds.

Thankfully, the pilot has a sophisticated instrument panel that helps guide our course. Birds, too, have a sophisticated set of tools for navigation. Besides using landmarks during the day, they use the rotation of the stars, the orientation of earth’s magnetic field, and the angles of polarized light at sunset.

New research from the Max Planck Institute for Ornithology in Seewiesen, Germany, has added weight to the hypothesis that homing pigeons (and probably other birds, too) use smell to navigate home. Every place smells a little different, and breezes coming from different directions carry that information to the pigeons. The birds can essentially create a smell map in their head that helps them navigate back home. Amazing! But I’m still glad my pilot is using a GPS.

Although humans only achieved flight when they stopped trying to copy birds, now that we’ve figured it out, engineers are looking back at the more experienced flyers to solve all sorts of problems. For example, jet aircraft engines used to “choke” at supersonic speeds due to air moving around the engine instead of through it. The peregrine falcon – which can dive at over 200 mph – provided a solution. Specialized cone-shaped bones near its nostrils, called baffles, deflect shockwaves of air and allow peregrines to keep breathing. Jet engines now have similar cones in their engines.

Despite the clouds, we found Chicago, and with our loon-like limited maneuverability, swung wide over the lake to start the landing pattern. As we slowed down to land, the plane used another bird-like feature on the wing. Nearing the ground, slats on the front of airplane’s wings dropped down. According to Wikipedia, this “allows the wing to achieve a higher than normal angle of attack – and thus lift – without resulting in a stall.”

On a bird, the alula--a small projection on the leading edge of the wing--serves the same purpose. It is essentially the bird’s thumb, and its three-to-five feathers can be moved freely. When flying slowly or landing, the bird can move the alula slightly upward and forward, giving it the same advantages as the airplane slats in slower or higher-angled flight.

Future airplanes may use a sharkskin-like paint job or butterfly scale-like coverings to reduce drag. Seabird-like moveable wings might improve efficiency with gusts. Humans continue to look to nature for more ways to improve our flight. Even rubber made from Kazakh dandelions may one day provide a more sustainable material for landing gear.

As the old-fashioned rubber tires bumped onto the runway beneath me, I was grateful for the chance to view the world from a new perspective. But I realized that my relatively effortless trip was made possible by years of innovation – just like the snow buntings’ effortless grace came only after eons of evolution.

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Friday, November 8, 2013

A Dandelion Smile

A chilly breeze whipped around my head. Even a pale sun peeking through racing clouds did not seem to improve the temperature. Head down, I hurried toward the post office. Then, a spot of color made me stop and smile. A single yellow dandelion and its star of vibrant, toothy leaves nestled into the snow-flattened grass.

I’ve always loved dandelions. They popped up every summer in the kingdom of make-believe that was my yard, and created a sea of sunshine in the farmer’s hayfield across the back fence. Every spring I still pick one of the hardy flowers to give to my mom for her late April birthday. Unless I’ve flattened it in a card to send through the mail, she still sticks dandelion in a little vase on the sill above the kitchen sink.

As a kid, I continued picking dandelions all summer long. I’d split the stems lengthwise and watch as they coiled into beautiful curlicues when dunked in cold water. I soaked the fuzzy blossoms in water and made “lemonade” that I never drank. I almost hyperventilated while trying to blow every parachuted seed off the stem to make a wish. And every t-shirt I owned was stained with little brown circles from the juicy stems.

Even today, despite my awareness that dandelions are invasive weeds, I can’t help admiring their tenacity. And I’m not alone. Buddhist monk, Thich Nhat Hanh, shared this poem (written by a student) in his book, Peace is Every Step.

I have lost my smile,
but don’t worry.
The dandelion has it.

So I smile whenever I see those cheerful weeds. Sometimes I even brave their bitterness and eat young leaves in salad. Other folks swear by the sap as a remedy for warts or foot fungus. Turns out, the dandelion may be more useful than I ever imagined!

The Kazakh dandelion (Taraxacum kok-saghyz, a relative of the one in your yard), is an excellent source of natural rubber. The milky sap in the root is so high in latex that one field of dandelions produces as much latex as the same size plot of rubber trees. In addition, the quality of dandelion latex is exactly the same as latex from a rubber tree, and can be substituted one-for-one in the rubber formulation. To top it all off, dandelion latex does not seem to trigger allergic reactions!

Russians discovered this amazing dandelion in the early 1930s, in Kazakhstan. They tried to develop it as a domestic source of rubber. During World War II, when the Japanese controlled the supplies of rubber from Southeast Asia, researchers in the United States, Germany, Sweden and Spain all jumped on the dandelion-rubber bandwagon. In the U.S. alone, land grant universities in 40 states conducted research on this lowly plant.

Most research came to a halt after the war ended in 1945. Today, an internet search for dandelion rubber reveals that at least three separate tire companies are partnering with research institutions to make this new source of rubber viable on a commercial scale. Germany's Fraunhofer Institute for Molecular Biology and Applied Ecology is working with Continental. Bridgestone is working with the Program for Excellence in Natural Rubber Alternatives at Ohio State University. Multinational tire manufacturer, Apollo Vredestein, also thinks dandelion rubber has potential, and is collaborating on the project with KeyGene.

Despite the many benefits of dandelions – they grow like weeds on many soil types, reproduce like weeds with lots of seed, and thrive in northern climates instead of sub-tropical forests – there are some obstacles, too. Dandelion juice transforms from a liquid to a solid on contact with the air – a process known as polymerization. This means that processors must use turpentine to chemically extract the latex from dandelion roots.

To eliminate the enzyme responsible for polymerization, German scientists at the Fraunhofer Institute engineered a special virus. According to a Discovery News article, “Once inside, the virus deleted the offending genetic sequence from the Russian dandelion's DNA. Pop the head off an infected dandelion, and the latex begins to flow freely.” (Watch out, Mom!  My shirts will have more than just little brown circular stains!)

It worked. But in Europe, creating transgenic dandelions is pretty controversial. Now German researchers are using traditional selective breeding techniques to accomplish the same thing. At the same time, Continental is working with the researchers to build the first ever commercial-scale processing plant. (Hopefully they are also developing ways to make sure the super-seeds don’t escape into our yards!)

Maybe in the future, that field of dandelions across the back fence won’t be full of weeds. It will be full of a cash crop, harvested by the same machines used to pull tulip bulbs. The sticky sap, once a stain on my shirt, will instead help my airplane land safely in Germany so I can go for a ride in a car with dandelion tires. That might even make me smile.

“What is a weed? A plant whose virtues have never been discovered.”

--Ralph Waldo Emerson

The Weird Ones

The scent of snow fills the air, and the hissing plops of wet snow falling off the trees fills my ears. The woods, and its inhabitants, are transitioning between fall and winter. It’s the same for me, as I jog down the road in my summer hat and winter gloves, wishing for ski season to arrive.

Early fall was a time of vibrant colors and lots of action. Colors have faded a bit now. If you have lived in the north for a while, you may have come to appreciate the subtle gold of a tamarack swamp, or the rich browns in an grove of oaks as they extend the fall color season. But have you ever stopped to think about how weird those two trees are?

Tamaracks are conifers, bearing their seeds in cones just like their relatives the pines, spruces, and firs. But conifer isn’t our first choice for describing pines – we’d rather call them evergreens. When we do that, though, tamarack doesn’t fit. It is the only deciduous (losing its leaves seasonally) conifer in Wisconsin. Oaks, in contrast, are in a group known as broad-leaf trees, most of whom are deciduous. Yet oaks cling to their leaves.

Why would a tamarack lose its needles? Why would a pine keep its needles? And why does the oak keep its dead leaves?

There is adaptive value in each strategy, otherwise they would not persist. Needles are really just modified leaves, better suited to low nutrient, low moisture situations. They have basically the same parts as a maple leaf, but everything is more tightly packed and protected. The stomata (pores for gas exchange) hide in a groove, protected from dry winds. A waxy outer layer helps to prevent water loss. By retaining green, chlorophyll-filled leaves all year, evergreen trees can take advantage of any warm days to photosynthesize, and save themselves the trouble and nutrient expense of growing new leaves each spring. They replace only about a third of their needles per year.

On the other hand, broad-leafed deciduous trees, like maples, grow large leaves with a lot of surface area for photosynthesis. The broad leaves also result in a lot of water loss. This is fine when it is raining, but not when it is frozen. Although trees use enzymes to protect leaves from freezing while they are still photosynthesizing, that only works for so long. Then, frost-damaged leaves would be a liability as an entrance for disease.

Why would tamarack combine the two strategies and lose its needles?
Well, we don’t know for sure, but my favorite theory is that it has something to do with how far north the tamarack’s range extends. On the Winter Solstice this year, Duluth, MN, will only have 8 hours and 32 minutes of sun. In Fairbanks, Alaska, near the northern edge of the tamarack’s range, the sun will shine weakly for 3 hours and 42 minutes. Most of the tamarack’s habitat is in the middle of that range. What good are green needles if there is little sunshine? By building more delicate needles that don’t have to withstand harsh winter conditions, tamaracks can save a little energy.

Likewise, what good are the dead, brown leaves of an oak, even with sunshine? Oaks are a broad-leaf tree, but, oddly, they hang onto their leaves until heavy snow knocks them off, or until new leaves push them out. Most deciduous trees (including tamaracks) cut their leaves off by growing a protective abscission layer on the end of the twig, and then encouraging the leaf to skedaddle with digestive enzymes or a new layer of cells.

In contrast, oak leaves start to grow an abscission layer soon after new leaves form, but do not finish the process until the next spring. Scientists call this retention of dead stuff “marcescence.”

Plant physiologists agree that marcescence is a juvenile trait, associated with young trees and newer branches. This makes sense, since the young aspens in the field near my house are still holding onto their leaves. And understory trees, which tend to be younger, always seem to change colors later in the fall.

Marcescence also may be juvenile in terms of evolutionary history. In southern regions, some oaks are evergreen. Our northern oaks may be in transition from being fully evergreen to being fully deciduous. Maybe they are not done yet…or maybe they like where they’ve paused!

Although there are tasty new buds waiting to come out in the spring, this year’s dead, dry, crinkly oak leaves are not very palatable, and that may deter deer and moose from nibbling on the new growth. The tardily deciduous aspens probably gain that benefit, too.

Another hypothesis is that the oaks are saving their leaves until spring. When the leaves fall, they will provide the tree with nutrient-rich mulch for the growing season, instead of the leaves decomposing throughout the winter. The leaves dangling from lower branches may also act as a snow fence, trapping extra moisture for the tree.

Of course, there is no way for us to know for sure just what the oak is “thinking” as it rustles its skirt of leaves in the middle of a blizzard. Nor do we understand what the tamarack is “planning” when it turns golden, and then bares its knobby twigs for the winter.

As with humans, the weirdest organisms are often the most interesting. At least, that’s what I hope, since some of you probably think I’m weird to be wishing for ski season in October!

For over 45 years, the Cable Natural History Museum has served to connect you to the Northwoods. Come visit us in Cable, WI, at 13470 County Highway M. The current exhibit, “Deer Camp: A Natural and Cultural History of White-tailed Deer,” opened in May 2013 and will remain open until April 2014.

Find us on the web at to learn more about our exhibits and programs. Discover us on Facebook, or at our blogspot,

Saturday, October 26, 2013

Woolly Weather

A blustery fall wind swept away any warmth from the pale sun. Brown and yellow leaves skittered across the pavement. As I bent down to dip my hands in the lake, my arm (wrapped in fuzzy fleece) brushed the seed head of a burr marigold—so named because the cheery yellow flower matures into a cluster of pokey stick-tight seeds. Yet another sign of the season…

Distracted, I meandered back toward the car, picking little two-pronged seeds out of my armpit as I went. Then...whoa!  Something caught the corner of my eye, and I pulled my foot back from its next step. There, in the middle of the parking lot, was a woolly bear caterpillar. Not the most exciting find, but it would have been unpleasant for both of us if my shoe had continued on its original path.

I’ve always enjoyed seeing these fuzzy, black and brown-striped critters. As a kid I tortured them—poking one to watch it curl into a ball…patiently waiting until it uncurled...and the poking it again. You’ve probably had your own encounters with these cute little critters, no matter what age you happened to be. A few years ago, while I was teaching in Maine, my class found a woolly bear’s hairy cocoon in the woods. The students just shook their head at my enthusiasm for the discovery.

Seeing this woolly bear didn’t strike me as anything spectacular, but I took some photos anyway, because a friend had asked me about the caterpillar’s famed weather predicting skills. My research turned up a great story about that, and so much more.

Back in 1948, Dr. C. H. Curran, curator of insects at the American Museum of Natural History in New York City, wanted an excuse to get out of the city and enjoy the fall colors. He decided that the question of woolly bears’ weather prediction skills needed some field research (sounds like a great excuse to play hooky from work to me!), and took his wife a nearby state park. They gathered as many woolly bears as they could find, and measured the sizes of the black and brown stripes. This was so fun that they invited friends the next year, and began calling themselves The Original Society of the Friends of the Woolly Bear.

For eight years they “gathered data” in the beautiful fall woods. At first, it seemed like they were on to something. Several years in a row, the brown stripes took up more than a third of the caterpillar’s thirteen body segments, on average. Folklore says that wider brown stripes forecast milder winters, and that did indeed play out for Curran. Then came the year that two groups of caterpillars in neighboring habitats gave opposing forecasts. That year, Curran gave up.

As it turns out, some scientists now think that the width of the brown band IS related to the weather—of the previous spring. Each time the caterpillar gets too big for its skin and molts, one black segment changes to a brown segment. So, a w-bear who starts eating early (they are generalist feeders who eat a variety of plants), during a mild spring, will have a wider brown stripe by the following fall. A caterpillar who gets a late start, perhaps due to snow in April (not that we know anything about that!), will likely have fewer brown segments before the growing season ends again.

So, with one riddle solved, we’re ready for another one. Why do you see so many woolly bears crossing the road this time of year?  To get to an overwintering site, of course! Like many northern critters (bears, for example), woolly bears are short-distance migrants who need to travel a little ways to find a nice place to spend the winter. And they can get there fast (for a caterpillar) traveling at 0.05 miles an hour, or about a mile a day.

Beneath a rock, under a log, in a bark crevice—almost any protected place will do for an overwintering woolly bear. Warmth is not a major factor, since these little guys will freeze solid, and thaw, and freeze again, many times throughout the winter. On a warm day, they may even get out and crawl around.

If a tomato spent the winter like a woolly bear, it would soon be mush. But woolly bears use chemicals known as cryoprotectants to safeguard living tissue against damage from freezing and thawing. Woolly bears who live in the arctic (the species we know as well as some relatives) may take 14 years to complete their life cycles. They freeze solid every winter, and grow just a little bit during each brief summer.

Our Wisconsin (or Minnesota) woolly bear only needs two years to complete its life. In spring, it will thaw and resume eating. Once large enough, the caterpillar spins itself a cocoon using silk and its own hairs. In two weeks, it metamorphoses into a pale yellow Isabella tiger moth. In another two weeks, the moth will mate, lay eggs, and die.

Tiger moths, in the family Arctiidae, are amazing, colorful creatures in their own right. Some tiger moth caterpillars eat toxic plants, just like monarch caterpillars, in order to protect themselves against predators. The toxin persists in the adult moths, who use bright warning coloration to tell potential predators that they taste bad. Since one of their main predators—bats—can’t see colors in the dark, the moths emit ultrasonic sounds to warn bats of their unpalatability.

All the moths are surely dead by now, and their offspring, the caterpillars, are racing toward their overwintering rocks. I hope the one I almost stepped on found a cozy place in the leaf litter. With snow in the forecast, I’m glad I overwinter in a house. I wonder how mild or harsh this winter will be?  I wish a woolly bear could tell me!